Add Distance to Table Info

Add distance to table if site coordinates are provided and sort the
table by distance.  If coordinates aren't provided, the column isn't
displayed.
Center "Distance from Site" for Selected Plane

Center "Distance from Site" under "Lat/Long" for selected plane.
Add flightradar24.com link
Merge pull request #24 from ddeitterick/add_distance_to_table

Add Distance to Table Info
Merge pull request #25 from ddeitterick/center_selected_plane_distance

Center "Distance from Site" for Selected Plane
Merge pull request #30 from tslocum/fr24link

Add flightradar24.com link
Merge branch 'master' of https://www.github.com/MalcolmRobb/dump1090 into socket_hang