Adding pre delete hook

[abhishekchandratre]

The use case is linking eyebrowse with projectile. Before removing window config, user can be prompted to kill his current project.

[abhishekchandratre]

Hi Wasamasa, I was heavy vim/tmux user, eyebrowse-mode allowed me to stick with Emacs and grok it better. Thank you for eyebrowse package :) -Abhishek

[wasamasa]

Great, now squash these commits into one and force push them.

[abhishekchandratre]

Thanks :) this helps. -Abhishek

[wasamasa]

Thank you very much!