OpenCS settings

EDIT5: included in this set of changes:

Feature #854: Add user setting to show status bar
Feature #1310: Rendering User Settings (partially complete)
Bug fix: Window dimension to include frame size and other decorations
Bug fix: spinbox to allow keyboard entry and also to set default values correctly
Fix checkbox to have on/off status
Add setting to enable/disable shaders
Add stylesheet functionality to views
Add Subview settings: minimum width, max subviews, reuse subviews
Add Scene user settings
Adjust filterbox margins
Signal scenewidget when user settings change