1.1.0: Fix problem with recent change on Viessmann's server

Viessmann change a bit the way of handling OAuth on their server.
With previous version(<1.1.0) you are getting now a "Call to a member function getProperty() on null" error message. This release fix this problem.
I have also fixed the isOneTimeDhwCharge and added startOneTimeDhwCharge method(thanks to the rogrun's feedback).
Reminder: Don't forget to update the bootstrap.php to point to the new version of the phar.