UI to enable/disable admin permissions

From Rob...

>  We have admins in hub. This is controlled by flag in member table in the DB. Currently only way to set/remove this flag is messing with the DB manually. Some UI for this would be better.

...via https://lists.57north.org.uk/mailman3/hyperkitty/list/57north-discuss@lists.57north.org.uk/thread/4WCY7N4D7UV7HMN4ZOFEDX45JWLFPLQ5/