Profiles for compiz' effect-levels

To avoid loosing a custom set of enabled plugins and plugin-settings compiz needs to support profiles. This support has to be provided via libcompizsettings. In addition to that profile-support will simplify the task of tweaking the other two sets of effect-levels "normal" and "extra", which can be implemented as two additional profiles. In the end changing an effect-level will just select a different profile.