updating maps when context has been deleted

[offtherailz]

When remove a context all the maps created in this context should be updated.

There are two options:

• Delete all the maps
• Update then to open in the default viewer

When deleting a context, we can prompt the admin to do a choice or automatically do one of the above operations.
By default we can update the maps to the default viewer.

This task requires this entry point on GeoStore to run:

geosolutions-it/geostore#205

[tdipisa]

Closed in favor of #5149