Support for Tag beckend

[tdipisa]

Introducing the concept of Tags for Resources in GeoStore with related filtering/search support as also available for other endpoints.
Tags should be provided via a new entity on the DB side with related services (cardinality is to the Resource table 1-N).

Assigned Tags to a resource should be also returned in the /extjs/search/list and /extjs/resource/{id} response payloads (see #379 and #380).

Tags should have at least the following attributes:

• FK to the Resource table
• Name
• Color
• Description

As for permissions, depending on the user role it is expected that:

• Admin can perform all CRUD operations on tags
• User can only list/filter tasks and assign them to a resource