- Add rule based thresholds
- Add safecommit to Jenkins

[Also correct some comments.]

The platform includes jshint as a development tool, and our
builds are enforcing a limit on total number of jshint violations.
This commit will enforce no new jshint violations on a per-change
basis, much like pylint and pep8 are enforced. So with this change,
we'll be enforcing our linting requirements consistently, regardless
of type of violations.

Also on Jenkins, runs quality task after installing jshint.

The old line:

    from path import path

produced pylint errors because of the baroque way that path.py defined
"path".  We tried to get them to change how they defined it, but they
deleted the name instead: https://github.com/jaraco/path.py/issues/102

(Jason then changed his mind, but this is a better way to use path.py,
it avoids the pylint error at least.)

This complexity metric is created by using radon (see changed files for additional
documentation links). This tool calculates cyclomatic complexity and provides a numeric grade
where a lower number is better (e.g., less complex).

JShint will be executed with paver run_jshint, which will use a defined set of
directories (likewise defined are directories to ignore). A limit can be imposed
on the total number of violations. Note that this change does NOT include adding
jshint to diff-quality or `paver run_quality`.

Leverages recent changes in diff-cover to reduce number of diff-quality runs

TE-555

This adds the -l switch, wherein a violations limit is passed in. For
example:
  paver run_pep8 -l 700

Will fail if more than 700 violations are found.

By default, this limit is not enforced (i.e. if the -l switch
is not passed into the command, then a limit will not be put
into effect for that run)