Contributers should be able to register for (some) activities

[Martijn Luinstra]

Hello AC/DCee,

since Arnoud is too lazy to mail you; he can't enroll for the Gala. As far as I know, donors are allowed to visit activities, so that would mean this is a bug?

With kind regards,

Guus Klinkenberg

[Jelmer van der Linde]

Change ::member_is_active to ::is_member or ::is_donor

And give a bit more attention to the error messages shown when trying to access any part of the sign up stuff. Also donors can now sign up. Fixes #100.

→ <<cset c1b9fa2a6fa4>>