Add Donor status

[Jelmer van der Linde]

Donors should still have access to the website but should be locked out of the almanak.

Proposed changes:

• Add a new 'donor' status to the type column in the leden table
• Allow donors to log in as normally
• Allow donors to change their own profile but not to see other profiles
• Deny access to the webalmanak to donors

Open for discussion:

• Deny access to the forum to donors

[Jelmer van der Linde]

Implemented in 19ea4f7.