Simple AppConfig wrapper for the AppFramework

9 out of 10 cases apps want to access their own appconfig. Hence it
would be nice not to have to enter the app id all the time. This simple
wrapper just passes on the appid in all calls.

Basically this allows for simpler code in the apps.

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>