Better guest reset plan

[erkyrath]

When a guest logs in for the first time, its desc and pronoun are reset; also all instance properties for its personal start world. But really we want all of the guest's data to be reset. If they visit a world, it should be pristine.

(The code is in create_session_guest(), tweblib/session.py.)

[erkyrath]

This should work the same way as the general instance-reset mechanism: https://github.com/erkyrath/tworld/issues/158

[erkyrath]

Also reset the guest's preferences.

[erkyrath]

If a guest instance has inhabitants, boot them. May have to force instance asleep first.

[erkyrath]

Repeating details from https://github.com/erkyrath/tworld/issues/158:

• Drop all instances for the guest's personal scope
• Drop all instanceprop entries that match these instance iids
• Drop all iplayerprop entries that match these instance iids
• Drop all portals that match these instance iids (shelves in the instances)

We don't touch the guest's scope, nor any scopeaccess entries. (If the guest was invited to a group scope, they'll keep that access. Guests should not be allowed to create group scopes.)

Then:

• Drop iplayerprop entries for the guest's uid
• Drop portals for the guest's personal portlist (don't add the starting portal, tweb does that)
• Drop all playprefs for the uid
• Delete player.guestsession

[erkyrath]

Done! Whew. To celebrate, I've removed the guest restriction on Salvanas.