Lightscreen 2.0

Finally, this is is a long time coming. Hopefully it's not terribly broken.

Changelog:

• Screenshot Previews.
• Screenshot uploading to imgur.
• History.
• Revamped area mode with resizing and improved zooming.
• Reorganized options menu.
• Naming improvements:
  • Preview in the options dialog.
  • Added the timestamp naming.
  • Configurable dates.
  • Customizable leading zeros.
• Linux compatibility.
• Many tweaks, fixes and miscellaneous improvements.