Implemented editing functionality for both focus types.
Optimized InvalidateRange() if the update spans over the whole view.
Now resets the cursor position/selection when the editor offset changed.
UpdateFromEditor() now takes the range of the size into account.
git-svn-id: file:///srv/svn/repos/haiku/trunk/current@6739 a95241bf-73f2-0310-859d-f6bbb57e9c96