dbus_interface properties requires impl From<&Value>

Currently, passing a some value to the property setter requires that the property is passed by ref or you end up with having to implement impl From<&Value> for T, see the test case added in !463 (merged).

I believe either:

• The conversion by ref should only needed when needed, maybe if the type is not a basic copy type?
• Never needed as I believe most of the time you don't want to pass a ref but rather by value?