fix #1242: check first if subtitles dir exists
Merge pull request #1245 from aronasorman/1242

fix #1242: check first if subtitles dir exists
setup english language on startup
installed_language_packs api now uses session['language_choices']
add api endpoint for refreshing language packs
refresh language pack list after language pack download is done
also refresh language choices when we first load update_languages
Merge pull request #1249 from aronasorman/1244

Add "en" LanguagePack on server startup, use cache of installed language choices
Tweaks to allow updating, specify type
tweak paths to work for all topic trees
Adding packagees, so PR #6 can be clearer
Merge branch 'develop' of github.com:learningequality/phase-2 into local_content_tools

Conflicts:
	kalite/shared/i18n.py
Merge pull request #3 from bcipolli/local_content_tools

Path updates and merge to the latest ka-lite code.