User management

[sbrl]

With an initial settings GUI coming online over in #69, it's time we dealt with another pressing problem: user creation & management. All the cool kids (like ownCloud!) have a user management interface with which you can create and delete users, and change their passwords.

Obviously the cool factor here is through the roof, so we should totally get one of these (not so new) fangled things for ourselves :P

[sbrl]

Giving the wiki owner (the administrator) the ability to change the list of moderators would also be awesome :D

[sbrl]

Done! I'm not sure we can reasonably allow the wiki administrator to update the list of moderators via a web interface at this time, as the $settings->admindetails_* settings aren't actually tied to any specific user account. We'd need to look at refactoring that in order to implement that.

To that end, I'm closing this issue now, but we can investigate that at a later date in a separate issue I think if the need arises.