Improvements to the dump.py script

* Uses the following instead of `os.system` (where applicable)
	- `subprocess.call`
	- `subprocess.Popen`
	- `shutil.copy`
	- `os.remove`

* Uses `os.path.join` instead of string concatenation
* Compresses the backups and provides an alternative
  compressed version of `aligulac.sql`