Fix and clean vtkWin32OpenGLRenderWindow class.

The fix concerns the window name (title): before this patch, the name
could only be set once the window was created. A default name
was provided and appears in the title bar.
The window name can now be set before the window creation as
under the X implementation for instance.

Fixed some nonsence code in GetPosition().

On the side, the code has been cleaned (coding style, useless comments...)

Change-Id: I9e47941a932b1137964f93c6929bc0d0a2971ba3
Merge topic 'FixAndCleanWin32OpenGLRenderWindow' into master

98fcc712 Fix and clean vtkWin32OpenGLRenderWindow class.