Reduce badnwidth at low zoom level: 'trick' the map into showing lower zoom levels.
For example, if the map is at zoom level x, show the tiles for x - 4.
I don't do this exactly.
This code has a low/high zoom level switch, at
the high zoom level, behave as before this commit; at the low zoom
level, trick the map into showing very low resolution tiles, so only a
few tiles need loading to cover the map area.
rename HIGH_ZOOM_THRESHOLD
Merge branch 'dev' of https://github.com/garvankeeley/MozStumbler into low-res-tiles

Rename MapActivity to MapFragment
Move the network receiver to its own class, and bind its lifetime
clearly to the lifetime of the MapFragment onStart onStop. Add lots of
guards against the activity disappearing on us.
Merge branch 'dev' of https://github.com/garvankeeley/MozStumbler into 2-level-low-res

Conflicts:
	android/src/main/java/org/mozilla/mozstumbler/client/mapview/MapFragment.java
	android/src/main/java/org/mozilla/mozstumbler/client/navdrawer/MainDrawerActivity.java
Merge pull request #998 from garvankeeley/2-level-low-res

Reduce bandwidth at low zoom level: 'trick' the map into showing lower zoom levels.