Replace existing custom ChannelHandler creation language with OGNL

[RoganDawes]

Current mechanism for defining ChannelHandler instances at each node in the graph is rather limited, and ignores many different ways that might be required to actually specify a handler.

Remove it, and use OGNL instead.

OGNL also supports use of a custom ClassResolver, which can be backed by a dynamic ClassLoader which can be used to place user classes on the classpath, rather than having to exit and restart Mallet.