Implement Indicator and IndicatorManager classes

This is still a WIP until I figure out what the MIDlet I'm testing is actually doing on a real phone.
Hmm. It seems like in the future we might run into problems if an app creates an Indicator but doesn't intend to append it (or will append it conditionally at some later time). Let's cross that bridge if we ever get to it; we can land this as is and deal with issues in the future if they ever come up.