Multiple Users Group Implementation + other fixes

This pull request close issues #57 and #58 and introduce a the concept of multiple usergroup assigned to an user.
An use can access to a resource if it is:
- The owner (the user who create the resource)
- One of the member of at least one user group that has permissions on that resource.

Note that:
- The permissions are different between **READ** (getResource) and **WRITE** operations (updateResource or deleteResource). **getAllResources** is available to any user hence it returns only ShortResource. **deleteAllResources** is filtered by role, only admin can use that service.
- If the user has no group assigned the behavior  is maintained as before for backward compatibility: The user can read all resources but cannot write on it

In order to understand the workflow check **insertGetDeleteAssign_UserGroupTest** and **updateSecurityRulesTest** tests in module geostore-rest-client (are online tests so a geostore running on port 9191 is needed).

**Know Problems**
The Services */search/{nameLike}* ( *getAllResources* ) and */search/list* ( *getExtResourcesList* ) returns any resources without check the resource grant