The blob is a set of type/value pairs which can be serialised to a byte
array for storage in the DB.

Redundant as it is always the same as totalBytes

* TapeFile::compressedSize is renamed to fileSize
* TapeFileWritten::compressedSize is removed, as it contains the same
  information as TapeFileWritten::size

Turns out that properly splitting the query with a "persistent"
temp table is ~2x faster than the full query.

cta-fst-gc now logs an error if it cannot list the contents of an FST filesystem or if determine the filesystem's sub directories

ctafstgcd.py no longer logs an ERROR when it fails to stat() a file that has been deleted by the FST