Follow up on code review:

* Renamed function for session id creation in manifest and stored dictionary of last_id, last_full_id and all_full_ids in the metadata so no parsing needs to happen. Added more comment to the manifest to explain the session id logic. Added `if` around session_id update flag, so flag gets set only once.
* Reverted tub test and created new tub writer test instead
* Removed shutdown hook from tub writer as it will be closed by the vehicle
* When session_id data gets inserted into the metadata, only modify the corresponding line (actually the seekable also modifies the lines below, there is still room for improvement in that method)
* Minor performance upgrades and improved timing in fast forward loop in UI