Send activity start/stop events to tag manager for issue #55

For review, here's an initial attempt at sending events to the tag manager when some activities are started / stopped. I used the .jar from https://dl.dropboxusercontent.com/u/3380376/GoogleAnalyticsServicesAndroid.zip (found at https://github.com/futurice/festapp-android/issues/54) and used the container file (assets/tagmanager/GTM-5XFNM5) from the example with the openScreen example.