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
Add pycharm helpers to gitignore
For a11y, modal dialogs and script templates should be hidden from
screen readers. Also, the mathjax message should be wrapped to prevent
non-IE browsers from complaining about a feature that is IE-only.
i18n word cloud LMS-2197
More than one dummy language
Latest eo strings, lots of small differences due to Dummy changes
Change name of bok-choy XML coverage report to avoid combining it with the unit test reports
Updated title and template for image modal html component

LMS-2215
Merge pull request #2528 from edx/sarina/lms-2197

i18n word cloud LMS-2197
Merge pull request #2522 from edx/markhoeber/image-modal-title-change

Updated title and template for image modal html component
Fix pylint violations
Merge pull request #2511 from edx/zoldak/pycharm

Add pycharm helpers to gitignore
Remove unused imports.
Merge pull request #2540 from cpennington/fix-pylint-errors

Fix pylint violations
Improved sequence navigation accessibility
Add Greek language translations