[ConsoleKit] multi-seat branch recent changes

[Ray Strode]

Hey Halton,

I've pushed a few changes recently to the multi-seat branch, can you
look them over and tell me things seem okay for you?

A summary of the changes:

- Emit SessionToAdd/SessionToRemove unicast only to the seat manager.
This is to deal with Marcelo's complaint on gdm-list
- Rename .disp to .display files
- Remove redundant "Seat" from "ManageSeat" and "UnmanageSeat" Seat methods
- Drop is-dynamic parameter from SessionToAdd signal
- Rename SessionToAdd to "OpenSessionRequest" (and SessionToRemove to
"CloseSessionRequest")
- Rename CkDisplayType to CkDisplayTemplate
- Add a new "type" parameter to seats (for Marcelo's NX integration)
- Start to document some of the changes

One chunk I haven't touched is making ck-dynamic into a more generic
ck-seat-tool as we discussed before.  Would you mind looking into
that?

--Ray