Add separate dealer reg page.

This adds a new URL, which is simply "preregistration/dealer_registration" - makes the link a bit prettier to hand out.

Also fixes #595.
This gives the exact calendar year in which the event takes place, as opposed to the configurable "year" value. We may ditch or change the configurable "year" value to be a bit more generic (like, "subtitle" or something), because its actual function doesn't really have to do with years.

Alternatively, we could go with "organization name" and "event name" because that seems to be how we're using EVENT_NAME vs EVENT_NAME_AND_YEAR.