Fix srts metadata, rename internal parameters to make logic more straightforward.
Make sure to yield all files in finding input po files.
Report khanload communication errors gracefully.
Merge branch 'develop' of github.com:learningequality/ka-lite into develop

Conflicts:
	kalite/i18n/management/commands/update_language_packs.py
Generators cannot be reused, and these generators are small, so turn them into lists where reused.
set percent translated to 0 when we don't have any phrases
generate {language}_metadata even if we have no po files
catch errors when removing nonmetadata from po files

Conflicts:
	kalite/i18n/management/commands/update_language_packs.py
fix syntax error (python2.6)
Merge pull request #1340 from bcipolli/langpack_fixes

Langpack fixes