Helps with small file sync #331
When I benchmarked this, it went up to 6 parallelism and
was about 1/3 faster than the previous fixed 3 parallelism.
Doing more than 6 is dangerous because QNAM limits to 6 TCP
connections and also the server might become a bottleneck.
Should also help for #4081
* Compute the content checksum (in addition to the optional
transmission checksum) during upload (.eml files only)
* Add hook to compute and compare the checksum in csync_update
* Add content checksum to database, remove transmission checksum
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.
