A LibraryBackend may be deleted while an associated LibraryModel object is using
it. An example is an async query running while a connected device is removed.
To prevent this, use a share pointer for the LibraryBackend.
This fixes one case where LibraryBackend is used after deletion. However, the
raw pointer is still passed around in several other places. These should be
evaluated on a case-by-case basis to insure that circular depencencies aren't
introduced.
Marcus Müller
Jim Broadus
John Maguire
Krzysztof Sobiecki