Added a close button on Tab likes FireFox style

Special Thanks to ParallelLoeter:

http://sourceforge.net/projects/dockpanelsuite/forums/forum/402316/topic/3901160
Target .Net Framework back to 2.0 and remove commented methods
Merge branch 'master' of https://github.com/dotAge/dockpanelsuite into gh121

Conflicts:
	WinFormsUI/Docking/Strings.Designer.cs
	WinFormsUI/Docking/Strings.resx
Added close button to document to better match VS2012 Light theme.