[Fixed] Specify default layout grid (#1296)

* [Fixed] Specify default layout grid

Previously users would see blank values for grid size
even though a default was applied.  Users will now
see default values for grid size which should prevent
them from accidentally changing grid size.

Fixes https://github.com/nasa/openmct/issues/1285

* [Fixed] Don't hardcode grid size

Remove hardcoded grid size per comments.

https://github.com/nasa/openmct/pull/1296#issuecomment-259231499

* [Fixed] read layout before initial refresh

Read the layoutGrid sizes from scope (when watch is registered)
before refreshing elements, to ensure that layoutGrid is set
properly.

https://github.com/nasa/openmct/pull/1296#issuecomment-259231499

* [Spec] Update spec to match

Update spec to trigger watch on initialization to ensure
layoutGrid is set.

https://github.com/nasa/openmct/pull/1296

platform/features/layout/test/FixedControllerSpec.js

@@ -147,6 +147,7 @@ define(
                     mockFormatter
                 );
 
+                findWatch("model.layoutGrid")(testModel.layoutGrid);
                 findWatch("selection")(mockScope.selection);
             });