Addition of 3 TinyMCE plugins

The following plugins added to toolbar in Edit of Unit:
 - fontselect
 - forecolor
 - image
MixedModulestore wraps most getters, update_item, delete_item
with code to translate between addressing schemes based on app
and persistence layer addressing scheme specification.

STUD-1206
Added test for defaulting use_locations
update_item and other refactorings continued
Review-driven changes (to-be-squashed)
fixed conflict between Annotator and internationalitation
Change name of bok-choy XML coverage report to avoid combining it with the unit test reports
Remove tabs.
Include the third-party wiki app into the i18n toolchain

We use pybabel to extract strings from third-party apps, put them on
Transifex, then merge them into django.po.

[LMS-1681]
Indicate where i18n tools are being run.
i18n fixes for wiki templates.
Tests should explicitly ask for English.
Use the latest django-wiki revision.
Keyboard events and ARIA markup added to speed control. Replaced anonymous event handlers by named functions. Menu stays open on mouseleave when a speed entry has focus. In that case, the menu can be closed by clicking anywhere outside of it. [BLD-402, BLD-363]
Do not translate checkbox values
Move tests related to views files into views/tests.
Remove unused methods.
pep8 cleanup
Add unit tests to handle duplicate user registration attempts
Remove unused imports.