Fix Bug #229: Android App crashes immediately on startup

- remove CLEAR_TASK flag from starting intents in application context
- replace demo tab with an activity to remove activity choose dialog
- start acitvitys with 'startActivityForResult()' to get called back when the activity finishes

Conflicts:
	clients/android/src/main/java/org/openecard/android/activities/IntentHandlerActivity.java