Introduce the new sort_key method. Replace the old multitude ones,
thanks to properties too.

...because it's the Pythonic way to do it.

A setter method always takes a parameter and does not return a value.

Rename 'set_stats_snmp' method to 'get_stats_snmp'.

The crash occurs while trying to unlock a password protected Glances
server (TypeError: Unicode-objects must be encoded before hashing).

Don't redefine built-ins. Unless it's wanted.

Empty sets evaluate to False.

- Remove unused import
- Fix double import
- Remove unnecessary pass statement
- Fix bad indentation
- Fix pointless statement

Use None as a default value.
See https://stackoverflow.com/questions/101268/hidden-features-of-python#113198
for more information.

Minor cosmetic tweaks.

Use logutils when running on Python 2.6.

Close #512.