Make tabs switch between different fragments

- Construct record and history Fragments.
- Create a tab listener that attaches and detaches the tab fragments.
- Dynamically add a MapFragment to record. You cannot do this
  statically, as child fragment support in Android sucks at the moment.
- Apply some configuration to the map.
- Save map state between "configuration changes" (eg. device rotation).
I've opened issue #5, to add checkstyle to the build. This should help us catch things like this quickly, especially if paired with travis ci.