Add ability to audit and clean up groups on Crowd

Just like you can clean up your sites with Jira¹, Confluence² and Bitbucket³, it would be great if there was a way to clean up a Crowd instance from groups that have no one in them or groups that haven't been modified in a while.

I am aware that Crowd already has one cleanup function to prune delegated directories⁴, but this additional functionality for groups would be very handy.

[1] https://confluence.atlassian.com/clean/clean-up-your-jira-instance-1018788592.html

[2] https://confluence.atlassian.com/clean/clean-up-your-confluence-instance-1026047969.html

[3] https://confluence.atlassian.com/clean/clean-up-your-bitbucket-server-and-data-center-instance-1026059920.html

[4] https://confluence.atlassian.com/crowd/pruning-delegated-directories-1055690249.html