Modify `makemessages.py` to add the keyword for i18n for handlebars files.
Undo the changes on `makemessages.py` and modify `trans_real.py` instead because using `djangojs` will not work because the .handlebars is re-formatted by `prepare_js_for_gettext()` like javascript.  The handlebars templates are actually similar to django templates except for the tag delimiters used.
Include the handlebars extension only for `djangojs` domain but process it like a Django template.
Update DJANGO-CHANGES.txt by adding diff in: `makemessages.py` so that we can identify what we changed.
Add diff in `trans_real.py` so that we can identify what we changed.
change footer to include version
Merge branch 'develop' into feature/2472-have-makemessages-scan-handlebars-files-to-extract-translatable-strings
change 'download' btn to 'Open PDF Reader'
fixed audio player play and pause button issue on Android tablet
fixed the video points jump to 750 issue
prettify PDF container and related content container
makeing sidebar title vertically aligned
Merge branch 'develop' of https://github.com/learningequality/ka-lite into develop-beta-language
Merge branch 'develop' into feature/2472-have-makemessages-scan-handlebars-files-to-extract-translatable-strings
Update the i18n file with sample instructions.
Adds 'get_leafed_topics' to return all topics in NodeCache that contain content.
Allow progress reports to flexibly accept playlists and topics to show progress.
Reinstates navbar option to show progress reports.
Merge pull request #2719 from rtibbles/user_progress

Re-enable User progress
Merge pull request #2698 from mrpau/feature/2472-have-makemessages-scan-handlebars-files-to-extract-translatable-strings

Modify `makemessages.py` to add the keyword for i18n for handlebars files.
Beta language packs checking