Fix missing message mystery (#669)

* Missing message investigation

* Delete suddenly appeared messages

*  Add IsDeleted check

*  Undo deletion

* Add metadata check to messageExists

*  Fix bug

*  Move sendRequest and ensure timer is stopped

*  Remove count check

*  Undo request deletion and only use StopRequest

*  Move MissingMessageAppeared to StopRequest

*  Force MissingMessageReceived triggering

*  Enable deadlock mutex for debug

*  refactor reRequest lock-unlock

*  re-enable messageExists check

*  Remove waiting for the timer to be stopped

*  Re-enable count

*  Move IO access out of the lock

*  Remove MissingMessageAppeared

*  Remove messageExistsFunc check

*  Refactor reRequest

*  Increase threshold and remove print

* 

 Fix linter warnings

Co-authored-by: Levente Pap <levente.pap@iota.org>
Co-authored-by: capossele <angelocapossele@gmail.com>