In order to initiate the conneciton, we should not send a GET on the
webdav URL because that is not a valid webdav command on a collection.
Issue #2911
* When folder config is used, other folder definitions are always
removed.
* Fix a bug with the wizard becoming stuck when 'skip folder config'
is used.
* Use a shared pointer to Account everywhere to ensure
the instance stays alive long enough for a sync to terminate
* Folder is now tied to an AccountState
* SyncEngine and OwncloudPropagator tie to an Account and use that
for all jobs they run
Issue: Since the setup wizard currently always replaces the
account, it will always wipe all folder definitions, even when
the actual changes to the account were minor.
