methods to add PUT and PATCH handlers

Now that tiscaf implements these methods, it can be interesting to have
an interface using these methods.
For example, to save user settings on by one, instead of sending and
retrieving the entire json setting object, one can patch a aprticular
setting by sending a JSON Patch according to RFC-6902
make user setting modification a PATCH method
start and register couch session if not existing

If no couch session is registered in the http session, it is created
while retrieving it.
It will be cleanup up when the http session expires
add possibility to login

using a username/password pair, one can authenticate into the system
add feature to log a user out