Add hooks for killing and creating groups
Add a hook for removing a frame
Call `*split-frame-hook*' after split is completed

Calling `*split-frame-hook*' in `split-frame-h' and `split-frame-v' is
premature, as the split isn't visible, nor detectable yet. First let
`split-frame' finish updating the layout. This is required when the layout is
saved when the hook is called.
Remove unused hooks