To be able to test the SyncEngine efficiently, a set of server
mocking classes have been implemented on top of QNetworkAccessManager.

The local disk side hasn't been mocked since this would require adding
a large abstraction layer in csync. The SyncEngine is instead pointed
to a different temporary dir in each test and we test by interacting
with files in this directory instead.

The FakeFolder object wraps the SyncEngine with those abstractions
and allow controlling the local files, and the fake remote state
through the FileModifier interface, using a FileInfo tree structure
for the remote-side implementation as well as feeding and comparing
the states on both side in tests.

Tests run fast and require no setup to be run, but each server feature
that we want to test on the client side needs to be implemented in
this fake objects library. For example, the OC-FileId header isn't
set as of this commit, and we can't test the file move logic properly
without implementing it first.

The TestSyncFileStatusTracker tests already contain a few QEXPECT_FAIL
for what I esteem being issues that need to be fixed in order to catch
up on our test coverage without making this patch too huge.