Get rid of Hooker, move DVTSourceTextScrollView to a swizzling class too

And fix a silly bug with the swizzling category when the class doesn't
override the selector we're swizzling.
Get rid of XVimTextViewProtocol

it's replaced by XVimView/XVimBuffer.
It's a nice reference of the things to have though.
Migrate scrolling and some drawing code to XVimView