Permissions - super-user

[hannesm]

For start, let's have a boolean field in the user record that specifies if a certain user is an administrator or not.

Only an administrator should be able to see users and settings (and also edit these).

The first created user is automatically an administrator, and an administrator (similar to active) should be able to grant and remove others administrative rights. Similar to "active", there shouldn't be a mollymawk instance where there's no administrator left.

[hannesm]

fixed by #39