core: batch db operations for group leave and delete

[spaced4ndy]

Changes in this PR:

• batches db operations for connection updates when deleting member connections
• batches db operations for unused contact deletion
• reworks bulk file cancellation and deletion
  • cancellation and deletion are split into different functions, some call sites only do cancellation (e.g. leave group), some others only do deletion (e.g. clear notes)
  • leave group api now does file cancellation
  • file cancellation db operations are batched in steps (getFileTransfer, update files to cancelled, set xftp files "deleted" flags)
  • other call sites in addition to group leave and delete also use reworked approach: clear chat, user deletion, chat item expiration, some call sites deleting only a single file (e.g. chat item deletion)
  • some other call sites deleting only a single file continue to use specialized functions such as cancelRcvFileTransfer: SMP file connections, cancel file api (the latter makes more detailed checks and some additional actions e.g. to reset file for re-download); can be further simplified if SMP and inline files protocols are deprecated
  • in batch cancellation FileChunkCancel is no longer sent for SMP and inline files for simplicity (as they are no longer in use and may be deprecated soon)