New QuickGUI Anchors

[Eric B Jones]

Add two Anchors for horizontal, Central Left and Central Right. Where one side remains the same and the other side scales to center.

Use ctrl-shift-f ANCHOR_HORIZONTAL_CENTER to find where you need to put the code.

After implemented, go through windows and find places we need to stick this thing.

[Eric B Jones]

Implemented in Windows code: ANCHOR_HORIZONTAL_RIGHT_GROW_TO_CENTER and ANCHOR_HORIZONTAL_LEFT_GROW_TO_CENTER