[All platforms]: Window.IsBorderless feature

new feature
[WinDX]: IsMouseVisible + IsBorderless

code for IsMouseVisible and IsBorderless properties
[WinDX]: Clean up

Now hides the cursor by default (XNA does this).
[WinGL/Linux]: Window.Borderless feature

new feature
[All platforms]: GameWindow comment rename
Fix rendertarget rendering (OpenGL)
[WinGL]: Fix for IsMouseVisible

This fixes IsMouseVisible on windows platforms, It is the only solution I could think of as the current Linux implementation works fine. This works just like XNA.
[WinGL]: Removed unused IsMouseVisible code

Linux now only uses that method
[WinGL/Linux]: Default to hidden cursor.

By default the cursor is hidden in XNA.
[WinGL/Linux]: Default to hidden cursor 2

Noticed that OnIsMouseVisibleChanged wont be called during startup when it needs to be.
Merge pull request #1403 from flyingdevelopmentstudio/develop

Fix rendertarget rendering (OpenGL)
Merge pull request #1389 from xanather/develop3d

IsMouseVisible + Window.IsBorderless
Merge pull request #39 from mono/develop

Merge back from develop