Improved documentation and removed useless constraint

Details:
- Improved UserManager and GroupManager REST API docs
- removed content-type constraint on group admin DELETE

src/main/java/org/gcube/data/access/storagehub/services/GroupManager.java

@@ -206,8 +206,8 @@ public class GroupManager {
 	/** 
 	 * Add an administrator to a group
 	 * 
-	 * @param id group id
-	 * @param userId user id
+	 * @param id group name
+	 * @param userId user name
 	 */
 	@StatusCodes({
 		@ResponseCode ( code = 204, condition = "Success."),
@@ -253,10 +253,10 @@ public class GroupManager {
 	}
 
 	/** 
-	 * Remove an administrator from a group
+	 * Remove an administrator from a group. The removed admin remains in the group as a <em>normal</em> user.
 	 * 
-	 * @param id group id
-	 * @param userId user id
+	 * @param id group name
+	 * @param userId user name
 	 */
 	@StatusCodes({
 		@ResponseCode ( code = 204, condition = "Success."),
@@ -266,9 +266,8 @@ public class GroupManager {
 	@ResourceMethodSignature(output = void.class, pathParams = { @PathParam("id")}, formParams = { @FormParam("userId") })
 	@DELETE
 	@Path("{id}/admins/{userId}")
-	@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
 	public void removeAdmin(@PathParam("id") String groupId, @PathParam("userId") String userId){
-
+	
 		InnerMethodName.set("removeAdmin");
 		
 		JackrabbitSession session = null;
@@ -302,7 +301,7 @@ public class GroupManager {
 	/** 
 	 * Get the list of administrators of a group 
 	 * 
-	 * @param groupId group id
+	 * @param groupId group name
 	 * @return list of administrators
 	 */
 	@StatusCodes({
@@ -339,8 +338,8 @@ public class GroupManager {
 	 * Add a user to a group <br>
 	 * <strong>Only users with <code>Infrastructure-Manager</code> or <code>VRE-Manager</code> role allowed</strong>
 	 * 
-	 * @param id group id
-	 * @param userId user id
+	 * @param id group name
+	 * @param userId user name
 	 * @return true if the user has been added to the group
 	 * @responseExample text/plain true
 	 */
@@ -391,8 +390,8 @@ public class GroupManager {
 	 * Remove a user from a group <br>
 	 * <strong>Only users with <code>Infrastructure-Manager</code> or <code>VRE-Manager</code> role allowed</strong>
 	 * 
-	 * @param groupId group id
-	 * @param userId user id
+	 * @param groupId group name
+	 * @param userId user name
 	 * @return true if the user has been removed from the group
 	 */
 	@StatusCodes({
@@ -437,7 +436,7 @@ public class GroupManager {
 	 * Get the list of users of a group <br>
 	 * <strong>Only users with <code>Infrastructure-Manager</code> or <code>VRE-Manager</code> role allowed</strong>
 	 * 
-	 * @param groupId group id
+	 * @param groupId group name
 	 * @return list of users
 	 */
 	@StatusCodes({

src/main/java/org/gcube/data/access/storagehub/services/UserManager.java

@@ -130,7 +130,8 @@ public class UserManager {
 	 *
 	 * @param user user name
 	 * @param password user password
-	 * @return user id
+	 * @return user name
+	 * @responseExample name.surname
 	 */
 	@DocumentationExample(" ...\n\nuser=nome.utente&password=passw0rd")
 	@POST