Add default handle method in Service base class

The default handle method will look for a supported_domains attribute
(a list), containing the supported domains. The subclassed service
class can of course override this if other means of determining support
is needded.
Rename Service's handle method to handles

handle can be ambiguous (i.e, not a verb).

Signed-off-by: Olof Johansson <olof@ethup.se>