Added 2 new config defaults:   basemap_type   basemap_xyzurl   This is in preparation for the new admin option to pick a basemap
default siteconfig: changed the default value of basemap_type to google, since clients here have been asking for that specifically
Changed default basemap type to Google Streets specifically   Added more specific basemap options to admin Map Services subpanel, e.g. Bing Satellite vs Bing Streets     The admin controller now actually saves these options, though tyhey do not yet have an effect
Added a default Bing Maps API key
Admin panel: map services: added some explanatory text for Bing Maps, indicating that an API key is reauired
Added the Bing ansd Google leaflet libraries
changed default BBOX siteconfig to center on NOrth America; sorry to be ameropcentric here, but the various APIs won't consistently handle -179,-89-179,89 for the whole world and I had to pick a place
Admin Settings: Map Services panel: Bing and Google map choices now fully implemented, including spiffy capability that the map will be destroyed and remade using your new basemap choice when you select; instant preview!
Almost final changes for uadmin-selected base maps: the desktop Map page, now supports this setting.  also, minor MVC cleanups: siteconfig was being accessed in template, instead of assigned to template by controller