[Matlab] Add basic nix.Tag documentation

- documentation for the Tag entity.
- rename addFeature to createFeature since it is an actual create method.
- update addFeature tests.
- rename removeFeature to deleteFeature since it is an actual delete method.
- update removeFeature tests.

Author: mpsonntag

+nix/Group.m

@@ -115,7 +115,7 @@
         end
 
         function [] = addDataArray(obj, idNameEntity)
-            % Add a nix.DataArray to referenced list of the invoking Group.
+            % Add a nix.DataArray to the referenced list of the invoking Group.
             %
             % idNameEntity (char/nix.DataArray):  The id or name of an existing DataArray,
             %                                     or a valid nix.DataArray entity.