Discontinue Client class

TicketUser class - Abstract class with auth token implementation
TicketOwner class - extends TicketUser

Add user ticket stats to EndUser class
Make collaborator extends ticket user  - necessary for authtoken support
Make Clientession extends EndUser

Allow variable replacer to call __call functions
Use ticket owner (enduser) instead of client.
Add EndUser lookup by email to TicketUser - returns a decorated user
Refactor/improve authtoken authentication backend.