Add date/time formatting settings

[byteit101]

Adds date and time formattings settings for the lockscreen. Depends on updated schema for cinnamon also: linuxmint/cinnamon#2182

[clefebvre]

This can now be done directly in cinnamon-desktop.

[clefebvre]

This is certainly an improvement but it's not ready to get in..

First, the date format shouldn't be specific to the lock screen. It should be defined globally in cinnamon-desktop.

Second, there's a huge debate over at Cinnamon as to whether this should be configurable and how.

For now in 2.0, I'm fixing the clock so it's properly localized but not yet configurable.

I'm keeping this pull open, because the minute this is solved in cinnamon, this pull will be very helpful here in the screensaver.

[mscheper]

This seems to be a reality in 2.6.13, but after 15 minutes of websearching, I still haven't found documentation about the schema. It's missing from the UI, and in the meantime, a link here, to the answer, would be appreciated.

[mscheper]

Turns out it just uses strftime. I probably should've guessed that, but with so many dumbed down new standards in the world today, this wasn't obvious. Documentation in the UI is necessary.