Port cream.config gsettings

[kkris]

So, this is a work in progress port from gpyconf to gsettings and not ready to be merged yet, thus open for discussion here.

How to test:
change in to the cream/config dir and type make settings which copies the gschema.xml file to /usr/share/glib-2.0/schemas/ and then executes glib-compile-schemas , so that gsettings can find it.
Then run python __init__.py which currently doesn't offer the API it should, but serves testing purposes.

Now to some implementation details:

As it turns out GSettings is actually quite suitable for our needs, which is mainly different seperated profiles and fast access. Each Configuration is identified by the schema and a path
The schema for example is org.cream.melange and each schema can have different paths, like /Default , /foobar , etc which represents our profiles. A change to a setting with the path /A does not change the setting in path /B

There are still some open questions, like what to do about our static keyword and some setting properties like min/max for number settings.
Also, right now every gschema.xml must contain two keys (profiles and profile-selected) which are used to save the profile names and whether or whether not this profile is currently selected. I'm not particular happy with that, hopefully there is a better solution.

Not implemented but not that difficult to add is the multioption and list setting.