Remove Answer and Request classes
Update interface-front-web.md

References to Answer classes deleted. Front exceptions (insufficient rights, non-existent stream...) now have to be caught by the website !
Users.AddStream changed to internal
[Front] Add new classes (draft)

inspired by api-draft-v2
Add Event constructor; fix XML comments.
Make Resharper happier :)
Update Stream.cs

New fields. Handle negative event ids. Methods do nothing or return
dummy events instead of throwing an exception.
Merge remote-tracking branch 'origin/master' into Front

Conflicts:
	EvernestFront/EvernestFront/Process.cs
	EvernestFront/EvernestFront/Stream.cs
Add key generation methods
Fix DummyEvent() and make private User fields private
Factor CheckRights
Fix calls to DummyEvent, make Source.Key internal
Refer to users and streams by their ID internally.
Add class UserRight
Rewrite Users methods without RightsTableBy-
Implement UserTable and add a new exception
Fix AddUser and CreateStream availability checks
Update front-web doc : move all public methods to class Process
Update interface-front-web.md
Move public methods to class Process