Implemented Coloring

Coloring for each category fully implemented. Corrected what points
were shown for a selected date span: now includes all offices that were
alive at any time during that span.
Implemented Color

Implemented point coloring, changed display of points for selected
brushes to reflect post offices alive at any point during the brsuh
Added Options

Added options for toggling different map views and more selective
estab/disestab options.
Got zoom to work and added transitions

Zoom works, and transitions added between established, discontinues,
and all options
Snapshot and Stacked bar graph

Added snapshot view, tabs, and a stacked bar graph
Merge pull request #6 from jhickcox/master

Snapshot view, tabs, stacked bar graph