Catch more variables errors

Display errors:
* when locale has extra variables
* when a variable is used a different number of times than reference
Merge pull request #187 from flodolo/python_errors

Catch more variables errors
Add firefox/android/index.lang and Privacy Tour

List of tracked locales is based on locales shipping in multilocale build on mozilla-aurora
https://hg.mozilla.org/releases/mozilla-aurora/file/default/mobile/android/locales/maemo-locales

List of locales for Privacy Tour is based on complete locales on last beta cycle