Catch ItemNotFound errors at the top of get_module, rather than in get_module_for_descriptor, to maintain previous LMS behavior

This cuts the number of queries in 6.002 courseware loads from ~650 to
~5-40. Still to do: cache CustomTag templates so that we only load them
once per request.

- set default queue in response type--don't use the default per-course one

- can't change the xqueue one because there's data that uses it
- we checked, and no one has sent out survey links that use the old sha1() format

doing this because we'll need the LMS to be able to send the anon student id to backend services e.g. for peer grading, and passing two different anon student ids to xmodule (one for xqueue, one for other uses) is just asking for confusion.

be sure to always pass in a course namespace - which can be just the location of the module itself since it has the same org/course pair - when rewriting links. Also, allow for an option parameter in get_module() to disable the wrapping of the module's HTML with the xmodule_display.html. This is needed for ancillary course content such as 'about', 'course info', which are now stored as xmodules, but should not be wrapped in xmodule_display.html as it breaks some styling

add to existing test cases to exercise the 'course extras as modules' work in the CMS import. Also add to the existing 'full' test data collection to include policy, tabs, etc.

make course about view methods render the about content as a module, so we get all the url rewriting goodness. Also, since we're now handling the url re-writing via the module get_html pipelines, we can remove the link rewriting inside the xmodules itself - which is good because there's a wierd bug in lxml.html rewriting

implement static tabs. rejigger .tar.gz import to do the re-namespacing as a post-processing step as we need to retain the original url_name during the import. Also, migrate the presentation tier to use module_render.py::get_module() to better unify HTML'ifying stuff

Make LMS access depend on which course run the access is occurring in, so that permissions can be based on the course run, rather than the whole course

- architecturally slightly questionable: the preview ajax calls goes to an LMS view instead of an input type specific one.  This needs to be fixed during the grand capa re-org, but there isn't time to do it right now.
- also, I kind of like having a generic turn-a-formula-into-a-preview service available

- courseware index view now redirects to most recent chapter, or first
- simplify the view a bit

* add a url that has an extra /{position} at the end
* pass it through to get_module

* also add a check for valid location in modx_dispatch

* All access checks now done for the "user" param, ignoring request.user
  - This matters for xqueue callbacks and for instructor view of student progress
* An effect of this change is that if a student couldn't see their own 'progress' tab,
  the course instructor won't be able to see it either

- only relevant in tests due to start dates
- still irritatingly intricate logic...