Channeler + test fixes + Poller fix

I've added a channeler type that wraps a zeroMQ socket around a receive and a send channel
Fixed some tests to not reuse the same inproc name, this caused the tests to randomly hang when zeroMQ found the old socket instead of the new one
Fixed code in the poller to correctly add all sockets passed to NewPoller, added code to test this in the tests as well