[Delete] Register delete all with action manager
[Delete] Include 'delete all' in objects menu
[Delete] Specify name of 'Delete All' action

Delete All is specified as the name for the recursive
delete action requested by nasa/mct#89.

This name is chosen for symmetry with the 'Save All'
action introduced in
770df79fdb732f8d60e013623dc1c85904c6ec50