Topic directive writes active topic to its scope

Instead of writing the active topic id to the root scope the topic directive now writes the active topic id to its private scope. The user of the topic directive can bind a property to that private scope property, through the ga-active-topic attribute.
gaMapController renamed to gaMainController
Switching topics updates body class
Remove semi-colon
Change body class in gaTopicChange listener
No need for parent/private scope binding
Remove superflous '1'
Merge pull request #248 from geoadmin/dev_topic

Topic directive shouldn't write to the root scope