Move reconcilation to sync thread and slim down C/C++ mishmash

[guruz]

void SyncEngine::slotDiscoveryJobFinished(int discoveryResult)

...since it can potentially take a quite long time (proportional to amount of files/folders) and then block the UI.

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[guruz]

Also: Port csync_reconcile to C++ so we can remove the two csync_walk_local_tree calls and have csync_reconcile directly create SyncFileItem.

[guruz]

I had quickly added Peak Memory tag here but that is wrong, the memory is already freed by then.
The peak should be after // The map was used for merging trees, convert it to a list:

[guruz]

This is partly done in 2.4.
Should still be moved to sync thread..

[ogoffart]

there is no more reconcile phase.