Merge pull request #589 from johnhaddon/rogueShaderParameterConnections

Prevented rogue connections being made to Shader "parameters" Plug.
Added plugs for specifying display style in View3D.

Upcoming commits will wire them up with UI elements to allow the user to change the display style.
Fixed unwanted scaling of Button images.
Fixed RunTimeTyped declaration for SceneView.

It was declared as deriving from View rather than View3D.
Improved MenuButton menu positioning.

It now always aligns the menu correctly, even when it doesn't have a frame, and also now uses the public Widget API to find the right location.
Fixed bug in Widget.widgetAt().

It was always returning the widget under the mouse, and not the one under the specified position. Also fixed WidgetTest.testBound() - it seems that we need to give Qt a number of idle events before it has got all the windows arranged on screen ready for testing.
Tweaked View3D colours.

Compress this in with the previous commit.
WIP.