Use events.emit instead of re-importing plugman each time

Looks like the re-import is no longer needed after this change
github.com/apache/cordova-plugman/commit/ae2ce7ac6325d1c6558365b4be82e5a8ff0983b9
the problem was probably due to
plugman.emit = emitter.emit
without binding the "this" for emit to the emitter.
Got no clue why the re-import is hiding that problem.
Use events.emit instead of re-importing plugman each time. Part 2.

See details in 961ccd7cd22d43f4b75145d916afec395dd0db56
The first part added the change only under src/platforms/
this one changes it everywhere else.
CB-6178 Plugman does not cache downloaded plugins

close #70
Add osx platform support