Allowed to access the wire method by mixing in Macwire trait

When building modules extending each other you need to repeat the import of MacwireMacros.wire method in each module. The only way to avoid it is to:
1) either keep all modules in one compilation unit, or
2) assign MacwireMacros to some val (like val injector = MacwireMacros) and then call injector.wire in all subtraits
Both those solutions have their drawbacks.

The proposed change allows to mix in Macwire trait (where the wire method is defined) in order to have that method directly accessible in subtraits.