require http-proxy > 1.5.1

1.5.0 has a bug preventing ws connections from working
remove ws workaround for node-http-proxy < 1.5
fix port expectation in api tests
ensure default target actually exists in tests
test proxying HTTP and websocket requests
Merge pull request #14 from minrk/nhp-1.5

require node-http-proxy 1.5.1