This prevents inapplicable tests from running when switching branches

If no default is provided, sass falls back to the system
default. This fails when the system default is not unicode because
various sass files have unicode characters in them.

Removed cleaning of reports folders, since this was
interferring with coverage reports generated
sequentially by rake test.

We used to specify specific rake test tasks so that we could run all of
them even if early ones failed. However, that meant that as new tasks
were added, they weren't being run on jenkins.

Now, there is a facility in the rake scripts so that tests can run using
the test_sh function, which will delay failure until the end of the rake
run, unless the TESTS_FAIL_FAST environment variable is set.

Furthermore, this reorganizes the jasmine test tasks so that we can run
those as part of `rake test` as well.

Added comments to tests.rake

Use coffee watch command to watch whole directories, so that it will pick up new coffee files as they are created

Using `task()` reopens the definition of the task, and all we really
need to do is get a reference to the task itself to invoke it.

The :browse_jasmine_<system> and :phantomjs_jasmine_<system> tasks
depend on the :assets task, which needs to receive both :system and
:env arguments. Therefore, new tasks (:browse_jasmine and
:phantomjs_jasmine) are created that do take :system and :env args.
The old :browse_jasmine_<system> and :phantomjs_jasmine_<system>
tasks now wrap the new tasks, passing in <system> as an argument
and 'jasmine' (for :env, since it's hardcoded to 'jasmine' in
django_for_jasmine()).

The LMS/CMS server startup depends on the :assets task, which needs
to receive :system and :env arguments. Since the existing server
startup tasks didn't take a :system argument, a new command called
:runserver is created that does take :system, :env, and :options
arguments. The old server startup tasks are adjusted to wrap the one
:runserver task that does all of the heavy lifting.

Rather than directly invoke command-line Python (and Mako) from the
assets Rakefile, or call an external Python script, use a Django
management command to preprocess all asset template files.

An "asset template file" is defined as a static asset file with a
file extension indicating that it needs to be run through a template
engine prior to Sass/CoffeeScript compilation or packaging with other
assets. The preprocess_assets management command will look through
all of the files listed in the `STATICFILES_DIRS`, preprocessing each
as needed. Preprocessing strips off the special template file
extension, creating a new file in the process.

Currently, the only variable accessible in an asset template file is
the `THEME_NAME`, defined in the settings.

to ensure we don't get coverage results from a
previous test run.

Added diff coverage reports using diff-coverage tool.

Capture the exit code of the Mako template engine invocation on
asset preprocessing and abort from the Rake task on failure. This
will prevent the LMS from continuing its attempt to start up,
preventing further configuration errors.

special case the db setup for the cms acceptance tests. We need the comment client database tables to be created since we're creating the DB from scratch

Per feedback from @cpennington. This way we'll only preprocess once,
even if the Sass compilation is invoked multiple times.

This commit adds the requisite settings and startup features to
enable integration of themes into the edX platform. It does not
yet provide hooks in any of the templates, but it does cause the
main `lms/static/sass/application.scss` file to `@import` a theme's
base Sass. Template hooks will come down the road.

CHANGELOG
---------
Define a new `MITX_FEATURE`, `USE_CUSTOM_THEME`, that when enabled,
can be used in templates to determine whether or not custom theme
templates should be used instead of the defaults.

Also define a new setting, `THEME_NAME`, which will be used to
locate theme-specific files. Establish the convention that themes
will be stored outside of the `REPO_ROOT`, inside the `ENV_ROOT`,
in a directory named `themes/`. `themes/<THEME_NAME>` will store
the files for a particular theme.

Provide a function, `enable_theme`, that modifies the template and
static asset load paths appropriately to include the theme's files.

Move the main LMS Sass file to a Mako template that conditionally
`@import`s the theme's base Sass file when a theme is enabled.

Add logic to the assets Rakefile to properly preprocess any Sass/
Mako templates before compiling them.

Start linting envs files, add task to only pylint errors, and move pylintrc file to the correct location

A better way to compute the hash, that gets the right hash after an install actually installs something.

This is to work around an OSx issue that causes EMFILE errors in the
default configuration.
Ref: https://github.com/joyent/node/issues/2479