Fix seek method to work for video.js (and renamed from seekTo).
Fix srts metadata, rename internal parameters to make logic more straightforward.

Conflicts:
	kalite/i18n/management/commands/update_language_packs.py
	kalite/shared/i18n.py

Conflicts:
	kalite/i18n/management/commands/update_language_packs.py
	kalite/shared/i18n.py
fix bug on missing variable