Adds spices integration (applet installer)

Installer should work with extensions, themes and desklets with minimal changes once we have the corresponding data exposed from spices website.

Installer currently unpacks zipfile into `~/.local/share/cinnamon/applets/{uuid}/`. If a localization directory named `po` is found, it is used to install localizations. If a `settings.py` file is found it is made executable.

Uninstaller removes localization if it exists, then purges the applet from the above folder. It also removes installed settings (per @mtwebster).

![screenie](http://dl.dropbox.com/u/2856016/applet-settings-11.png)