Simplify the Users table (!)

[dgoerger]

Right now in the Users database table we have the following columns:

id, login, first_name, last_name, nickname, phone, email, affiliation, is_banned, is_admin, is_checkout_person, created_at, updated_at, adminmode, checkoutpersonmode, normalusermode, bannedmode, deleted_at, terms_of_service_accepted

IMO we should consolidate is_banned, is_admin, is_checkout_person into:

type => 'admin', 'checkout', 'normal', or 'banned'

This way we could avoid the ludicrous (although theoretically possible) situations of Banned-Admins and Admin-Checkoutpersons (there might be a validation against these??), and also make our codebase more extensible should we or anyone else decide in the future to add / remove user types. It would also make my implementation of #6 (CSV import) much simpler for assignment of user types..

[An initial thought on this: Map NIL, (blank), 'patron', and 'normal' to all mean the same thing, so for CSV import admins have some flexibility / freedom from jargon.]

Also,

adminmode, checkoutpersonmode, normalusermode, and bannedmode

should either be similarly consolidated or else completely moved to the session (ideal).

[austinczarnecki]

I'm redoing the rspec tests as I make these changes, but it's also going to break part of the seed script. Sorry @mnquintana, I'll leave that fix to you!

[austinczarnecki]

Also fixed a bug with the page shown after importing users.