fixed error when no center &  no geolocation

[MOD] Fixed bug with directive when no center was set no geolocation
could be found
[ADD] Added option „fallbackcenter“ to be centered in on when no center
was set no geolocation could be found
Changed fallbackCenter to geoFallbackCenter
Merge pull request #52 from AlexandreKilian/master

fixed error when no center &  no geolocation