RTL/Arabic support

- LMS, CMS and Common support for unicode Arabic I/O.
- New RTL sass files for both LMS and CMS and some fixes.
- Statements added to check for availability of other languages yaml files.
- Added logic in html to load RTL css on language change if bidirectional.
- Added a language change link to switch between Arabic and English versions of the platform.
- Added set_lang url with view definition to perform language change.
- Added new variable to common.py "ENABLE_LANGUAGE_CHANGE" in both LMS and CMS to enable/disable language change.
Adding @abdoosh00 to AUTHORS file