- it is not enough to rely on the parent information of updated files
because that misses files and folders that were completely removed
(even from trash)
- don't use folder/get_content but rely on parent information
- add many more debugging information and sanity checks
- ignore trash
- correctly update local device revision using device_response
- remove "visited" member and change housekeeping function to check for
consistency of parents and children (and retrieve fix from remote if
necessary)
- print key and parent key in the debugging function
- check for remote updates on every fs function
- introduce global defines for key and filename length
- add parent member, getters and setters to file.h
