cm_crowdin: optimize the script

PS1:  Fix duplication of code
PS2:  Fix commit info
      Simplify code structure of commit creation
PS3:  Fix wrong comparisons
PS4:  Simplify commit creation further
      Simplify get_caf_additions()
      Add the default branch as a shared variable
      Simplify the removal of empty translations
PS5:  Fix whitespace error
PS6:  Fix commit message
PS7:  First steps to integrate JS website translations
PS8:  First full support for JS translations
      More comments
PS9:  Determine default branch by looking it up in android/default.xml
PS10: Rebase
      Rename script to 'crowdin_sync.py'
PS11: Add initial support for command line arguments
PS12: Rebase after latest changes
PS13: Fix arguments (parsing)
      Fix determination of default branch
PS14: Additional fixes
PS15: Rebase & cleanup
PS16: Ready to merge

Change-Id: I1a1a108f7f67cb51cb27cc16f9f333e1e09a8520