WMS layer support

Added some comments in the merge request.
WMS also allows two optional parms `VERSION` and `STYLES`, some WMS services even require them to correctly load maps. To make the WMS support more complete, it would be nice to also add an option to provide these two params in the custom map layer configuration.

Added two last comments in the merge request, after resolving them this will be ready to be merged.

Merged and released in https://www.drupal.org/project/farm_map_custom_layers/releases/1.1.0 → .

Automatically closed - issue fixed for 2 weeks with no activity.