cli: Add a summit-admin pause `some message` feature

In the case where multiple people can access the summit admin interface, it might be helpful to have the `pause` command accept a message describing *why* the pause is in effect.

This should then show up on all admin related commands and cause the commands to prompt if they would serve to "break" the pause in some way.

The message should probably also show on the webui as "Paused: the message"