Kolibri

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- Update all user logging related timestamps to a custom datetime field that includes timezone info
- Added daemon mode (system service) to run ``kolibri start`` in background (default!) 1548
- Implemented ``kolibri stop`` and ``kolibri status`` 1548
- Newly imported channels are given a 'last_updated' timestamp
- Add progress annotation for topics, lazily loaded to increase page load performance
- Add API endpoint for getting number and total size of files in a channel
- Migrate all JS linting to prettier rather than eslint
- Merge audio_mp3_render and video_mp4_render plugins into one single media_player plugin
- KOLIBRI_LISTEN_PORT environment variable for specifying a default for the --port option 1724

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- User experience improvements for session timeout

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- Prevent session timeout if user is still active
- Fix exam completion timestamp bug
- Prevent exercise attempt logging crosstalk bug
- Update Hindi translations

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- Fix bug that made updating existing Django models from the frontend impossible

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- Fix various exam and progress tracking issues
- Add automatic sign-out when browser is closed
- Fix search issue
- Learner UI updates
- Updated Hindi translations

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- Frontend and backend changes to increase performance of the Kolibri application under heavy load
- Fix bug in frontend simplified login code