Correct some verb tenses in the French translation

"Met en pause" looked particularly odd in the rendering progress dialog
Added Serbian translation
Updated Czech translation
Updated Czech translation
Updated Czech translation
viewer: fix alignment
viewer: Small code and comment cleanup
medialibrary: Fix the import progressbar to show translated text properly

Fixes bug #709537
Updated French translation
check: Present a human-readable error when gst-python is not working properly

This is 1000x better than the cryptic traceback users get when pygst is missing
check: Move dependencies to a single location and document for packagers
PEP8 compliance fixes in settings.py and render.py
check: Clean up the soft dependencies constants mess

This file is meant to make the packagers' job easier,
so it must be as legible as possible.
Releasing Pitivi 0.94 "Tricks or Tracebacks?"
Updated Czech translation
Updated Polish translation