Fix UI internationalization
Review Request #123254 - Created April 4, 2015 and submitted
This connects i18n calls to catalogs so that translated strings are actually shown in the UI.
Also fixes message extraction problems that caused some messages to not be extracted.
Looked at Muon Discover and Muon Update Manager. They appeared as mostly translated. For untranslated parts there are extraction fixes. Didn't test Muon Package Manager because didn't know how to test it in Arch Linux without installing some apt stuff.