Allow non-artist registrations

[chmarr]

Currently, registration process assumes only artists register, and thus always ask for full personal details. These are not necessary for agents.

Change as follows:

• Registration on the website asks for Name and e-mail address. This creates the "User" and "Person" objects, but with a unusable password
• emails confirmation, including the ability to set a password.
• On login, an option to register as an artist is displayed. Clicking this goes through the process of completing the personal details, selecting an artist name and agreeing to the art show rules, selecting panels and then making a payment. At the end (or if the process is stopped), a sample page with arrows indicating all the points.
• The "Top level" page contains links to edit personal details, register as an artist (if not done already), register an additional artist name, as well as a list of the artists currently linked, or linked as agents.

It may be desirable if the "register additional artist name" should be enabled per-artist, and initially showing a "If you wish to register an alternate artist name, please contact the art show manager."

Under the "Agenting For" section, say "If you intend to act as an agent for an artist, please have them add your login name to the "Agents" section of their artist page.

Under "register an artist", there should be "I am creating this account on behalf of the artist", which will prompt to create additional User and Person details. Workflow to be determined.