Add switches for rclone cleanup

[aetonsi]

What is your current rclone version (output from rclone version)?

rclone v1.52.2-198-gaedc8623-fix-4395-list-bwlimit-beta
- os/arch: windows/amd64
- go version: go1.14.4

What problem are you are trying to solve?

rclone cleanup is currently described like this:

Clean up the remote if possible. Empty the trash or delete old file versions

I'd like to run rclone cleanup on a remote to just empty the trash, or just to remove versions history.

How do you think rclone should be changed to solve that?

A solution would be to add a couple of switches, something like this:
rclone cleanup --only-empty-trash
and
rclone cleanup --only-remove-file-versions

[aetonsi]

Also, these switches should take into consideration the possible additional effects of #3964