Searchbox improvements

Added radius to Plot function to allow plotting circles at specific
coordinates, rather than just points.
Improved keypress event handling to allow searching by pressing enter in
search box.
Updated URL for Leaflet API documentation
Implement gmeInit()

New mechanism for starting up GME.
`gmeResources.scripts.common.gmeInit()` includes initiation code that is
generic to code modules, but has to wait for the JQuery or Leaflet APIs
to load before it will work.  Page-specific init code is still in the
`gmeResources.scripts.loadPage()` scripts.
Version 0.7.2

Version bumped for release.  Parameter added to vary update message.