Right now the form lets you define the fields where the geometries are
stored (either in a single GeoJSON field or a pair of lat/lon fields).
When adding features, if wrong geometries are found (ie wrong field
values), the process will stop and an error notice will be shown.
Added new listeners to refresh the markers whenever a document(s) is
added or removed, or all documents are reset. Instead of recreating
everytime all markers, only the necessary ones are added or removed.
The view will check for a set of default field names to see if there is
a field containing geometries in GeoJSON format. If not, will check
similarly for a pair of fields with lat/lon values.
Basic map view that plots points into a Leaflet map. Right now only
models with two "lat"/"lon" fields are supported. Some problems
regarding zooming to markers bounds when div not visible.
