Use a QSharedPointer to keep the same ownership and
continue passing the SyncFileItems as a const& when
ownership isn't taken. This allows sharing the same
allocations between the jobs and the result vectors.
This saves about 20MB of memory (off 120MB) once all
jobs are created.
* 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.
