tracker-extract: Use libz to process ps.gz files
Process ps.gz files using GZlibDecompressor instead of spawing gunzip. Because tracker-extract runs the file parsers inside a seccomp sandbox, spawning an external process during parsing is not a good idea because it leaves us with little control on which syscalls are used.
Also added some functional tests for ps and ps.gz files.
Closes: #61 (closed)