General worldmap plugin improvements

* Use _LAT and _LONG attritubes as alternative to _LOC_LAT and _LOC_LNG
  They are used, for example, by Nagvis GeoMap maps:
  https://clarin.fz-juelich.de/nagvis/docs/en_US/geomap.html
  It's a good way to keep compatibility with no user interaction

* Get and check valid coords refactoring
  Two new functions for this purpose in page and widget routing
  instead of using the same code

* New configuration variable: only_geo_hosts
  Let the user make the decision to draw only hosts with geo attributes
  Worldmap will not work in a huge infrastructure with more than 10.000 hosts
  placed in the same default point (beleive me, it doesn't work)