VS2012 Theme enhancement (in Demo project)

This pr provides a possible solution to the issue #174. Its goal is to capitalize main menu text in order to be a bit more VS2012-like.

I first tried to tweak the VS2012Renderer, but this proved to be the wrong path. 

I provide here a simple VS2012ToolStripExtender that's in charge of assigning the menu (or toolstrip) it extends the  VS2012ToolStripRenderer as well as capitalizing menu text. Because the extender remembers the original menu's text, it can be reverted when the current style is not VS2012 any more.

Note that this modification only affects the DockSample project.

Hope this helps.