Toggle variable for save hook clean up

Useful for making changes to files from other people's projects
Install org mode from git repo (not elpa)
Rework org agenda fullscreen advice

With previous advice, window configuration would not be restored
correctly if the agenda buffer was refreshed. This can be avoided if
restoring the window configuration is left to org mode (with
`org-agenda-restore-windows-after-quit'). There isn't a fullscreen
option in `org-agenda-window-setup', so `org-agenda-list' still needs to
be advised to delete the other windows.