update netty 4 version; close channel before waiting for the closing to finish
don't use pooled buffers in netty-websocket-transmitter
implement keep-alive in netty-websocket-transmitter
bugfix: multiple listeners were registered when elements were moved between ObservableLists
bugfix: added a way to ensure only one listener is added to a property at the whole time
- before, multiple listeners could be added under certain circumstances
- added new test to ensure the correctness of the listeners
support for http header parameter
Merge remote-tracking branch 'michael/bugfix_multiple_listeners'
deduplicate some test code
Merge remote-tracking branch 'denny/http_headers'

Conflicts:
	transmitter/netty-websocket-transmitter/src/main/java/de/saxsys/synchronizefx/nettywebsocket/NettyWebsocketClient.java
Temporary disable problematic test until it is fixed
[maven-release-plugin] prepare release SynchronizeFX-0.2
[maven-release-plugin] prepare for next development iteration