Create a mobile specific ui for the topic chooser.

If the screen width is small (uses visible-lg/hidden-lg from
bootstrap) display the topic chooser as an HTML select instead of a
dropdown list. The HTML select is moved inside the catalog panel.
Only display the topic select in mobile.html
Minor templateUrl function refactoring in gaTopic directive
Document the need for the scope.setActiveTopic function
Depends on pascalprecht.translate
Merge pull request #272 from geoadmin/dev_topic_chooser_select

topic chooser in mobile mode