Simplify settings dialog CSS

Stop the settings dialogs from requiring special styles on the
mx_Dialog which required passing in a classname from anywhere the
settings dialogs were opened (although this still requires
static=true). Some of the things have now been adopted for all dialogs
(border-radius), others have been moved to within the dialog content.

res/css/structures/_TabbedView.scss

@@ -91,4 +91,4 @@ limitations under the License.
     flex-grow: 1;
     overflow: auto;
     min-height: 0; // firefox
-}
+}