- Changed IImportChanges interface to use an SyncFolder object on
ImportFolderDeletion, changed all implementing classes to work with the
new parameter to allow clean rewriting of ids for backends.
- Expose folderid <-> backend-folderid conversion in both directions via
DeviceManager, saved in the ASDevice contentdata. 
- All folderids passed to the backend, are rewritten to the
backend-folderids, where all processing operations are done (as is) on
the new/short AS folderids.
- Never save ASDevice data when doing Ping, as on hierarchy changes
there will be race conditions between, e.g. FolderCreate and the running
Ping request, where Ping potentially wins writing this information (risk
of inconsistent AS folderids). The ASDevice is only changed because
during hierarchy verification new folders get a new AS folderid. This is
not used anywhere and really done on the following FolderSync operation.

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