Add entry markers to map

Implement gzip transport encoding, JSON stream parsing and parallel
asynchronous geocoding for an optimal user experience.  Needs cleanup
and more features.
Minimal refactoring
Show short description in marker info window
Skip entries with close_date parse errors in ListActivity
Skip closed entries in MapActivity
Source code cosmetics
Integrate MapActivity into menu, fix activity title
Add GSON license to AboutActivity
Update TODO