improve type safety when dealing with SynchronizeFX commands

Replace "message" with "command" in the documentation and the code.
Update README of Sliderdemo

- Updated the readme of the Sliderdemo for the new Step-builder to create the client and server instances
- Removed deprecated Builders for the creation of UI controls
Merge pull request #24 from lestard/master

Update README of Sliderdemo
provide the number of currently connected clients to the user
https://github.com/saxsys/SynchronizeFX/issues/23

Added support for replace operations in Lists.
https://github.com/saxsys/SynchronizeFX/issues/23

Added GPL header at ReplaceInList und ListCommand.
Merge pull request #25 from mthiele/master

https://github.com/saxsys/SynchronizeFX/issues/23
fix checkstyle and javadoc issues
make clear operations on synchronized lists work correclty #18
synchronized fields thats type extend supported property types #17
silence the netty debug log in the pinboard demo
start implementation of self repairing single value properties #16