Latitude longitude filter

Latitude/Longitude filter:

This filter let you define points and a radius in order to define areas. Then, the filter could discard bid requests not belonging to those areas.

Agent config example to use the filter:

{
...
"latLongDevFilter": [{"lat": 37.123, "radius": 15.5, "long": -92.456}]
...
} 

Should be added as a constant to the Priority enum. Makes it easier to see the ordering of all the filters since everything is in one place.