Add variable to toggle Extent Filter on Search Page

[arhote]

The extent filter uses a leaflet tile map in order to filter results based on the contents shown in the map. This map has to reach out across the open internet in order to properly access the tiles.

For some deploys this is not ideal, as it is not possible to access the open internet due to firewalls or other restrictions. As such it was determined that simply disabling the filter was the best way forward for those types of networks.

[voidspooks]

Appropriate changes have been made to cookbooks.