Add option to use core permissions to restrict user activities

[mrenvoize]

We closed issue #2 with an option to limit users to a config file-driven allow list. I'd still, however, like to add the option to control users using the core user permissions system and I'm working on bugs in core to allow for this.

[lizrea]

good feature I think

[mrenvoize]

I'd still love to add core handling for plugin permissions, but that'll take a while.

So, I've added a picker list to the config page to allow plugin administrators to set a list of users who should have access to the actual tool.