Show list of registrations for event

[matthijskooijman]

It would be good to offer a list of registrations for an event. There is two usecases:

• Show participants of an event who they will be participating with.
  This probably really needs to happen and show full names, since this has some safety implications.
• Show potential participants who is registered.
  This is is less necessary, but would be nice to have. One can say that this can happen outside of our system in the regular social channels, but there is a chance here for us to facilitate this process, rather than effectively forcing (potential) players to resort to using Facebook for this (which is probably the only feasible alternative atm).

There is also the question of whether to show fullnames or abbreviated (last)names. The latter is mostly needed for people that do not want to be Googleable, which should be sufficiently covered by putting the registration list behind a login.

The plan is to:

• Add a registration list, which is visible to all logged in users.
• Show fullnames by default.
• Prepare a "display_name" field that can be set by staff in case someone really objects to publishing their name.

At a later stage, we could further facilitate changing this displayname (e.g. by having a checkbox "hide my lastname", or offering a few options, etc.).

[matthijskooijman]

See also #87 about limiting access to (among others) this view when e-mailaddress is not verified.