* Rewrite the backend manager.
This creates a new more logic backend manager that handles all backend operations.
For each top-level operation, there is now a single backend manager instance that is passed to sub-commands.
The internals of the backend manager are now rewritten to use async logic instead of threading.
The design uses a single task runner that dispatches operations and honors concurrent settings and limits from one place.
The logic for each operation has been moved into a separate files/classes to make it easier to understand each operation.
This fixes#5804
* Fixed a few issues with not awaiting tasks
* Fixed not creating empty databases
* Fixed an issue with hashes not being recorded on download
* Reworked the download logic to avoid attempting to decrypt the file if it has been modified.
* Review fixes
* Renamed db collector to better reflect the purpose.
* Review fixes
* Simplified task control by having all logic in a single class and using async control mechanism
* Fixed the tests
* Made the marking of a backup partial explicitly communicated if the enumeration process is stopped.
* Added support for pausing active transfers
* Introduced transfer token to abort operations.
* Updated the way LiveControl is emitting events.
* Retains the paused state of the server across reboots, this fixes#5760.
* Reworked the way throttle speeds are propagated through LiveControls.
* Added option to pause transfers in the UI.
* Removed throttle settings from the LiveControls class so it is exclusively handled by the ApplicationSettings.
* Removed `thread-priority` as it does not work at all when tasks are used.
* Fixed the stop dialog and API to only support stop and abort.
* Removed unused variables
When support for parallel uploads was implemented, we overlooked a case
where a failed put of a dblock file is retried with a different
filename. In this case, an instance of TemporaryIndexVolume was created
in the DataBlockProcessor or SpillCollectorProcess prior to the
attempted put. The put would fail, and then retried with a different
filename. While the Remotevolume table in the database would reflect
the new filename, the TemporaryIndexVolume still contained a reference
to the old dblock filename. This would cause issues in direct restores,
etc., when the referenced dblock file could not be found.
Now, the TemporaryIndexVolume is only created after the dblock put has
completed.
This addresses issue #3932.
Encrypting, hashing, and creating index volumes are now done
in the DataBlockProcessor and the SpillCollectorProcess. This allows
uploads to always be transferring data and not have to stop to create
a file, encrypt data, etc.
