clipproperties: Add additional title clip properties

Currently, the title clip property menu does not support changing a title clip's drop shadow nor text outline color. By default, title clips have a drop shadow enabled and a black text outline color.

We have added a checkbox for the drop shadow, and a color button/picker for the text outline color so that filmmakers can now change these two properties.

Note: We had to "Hack" GES to expose the draw-shadow property. The MR for our GES change was merged successfully, so our feature will require the latest GES.