Add translator service

Wraps angular-translate. Closes #305. Actually a nice API.
Translate complete comments plugin to German
Activate angular-translate once and for all
Add flags for translateLanguage button
Minor translation change
Allow a callback fn in translator
Start to exchange translate filter with translator
Fix unusedTokenHighlighter translations
Lots of translations I
Translate saver
Translate history plugin
Translate MainCtrl
Fix MainCtrl spec
Move angular-translate from main to core
Translate commentFilter
Translate settingsTrigger
Translate dependencyTree directive
Refactor dependencyTree translations
Avoid loading bug of language flag

Need to pass the full path to ngSrc, otherwise a race condition might
happen, where an empty ".png" is tried to get obtained.
Updated collapsed navbar buttons titles