move to the new Maven build exclusively for the 0.30 release

As many of you are aware, we have been working on new Maven builds for the
Java components...

Short version:

I would like us to begin using the new Maven builds for the Java components
exclusively, removing the old build system from trunk and updating the
version in the 0.28 release to signal that it will be removed in 0.30.

Additional detail:

The Maven build is now able to do all of the core build and test
functionality the old build system does, plus some things it cant. While
there are no doubt still some finishing touches we can perform to improve
usability further, I think these would be best achieved through actual use
and evolution by everyone.

I have been merging the changes from trunk such that the 0.28 release is
going to ship with a near-parity preview of the current trunk Maven build
for the main Java tree, simply requiring an explicit flag to enable it. I
am keen to avoid further overlap of having multiple builds systems. In
particular I think there is reduced need for such overlap as there was for
say for the C++ build systems in the past, because unlike that situation
the source code and its build process are typically not part of a users
primary interaction with the Java components; this will mainly only affect
the people developing Qpid.

There are some instructions on using the new Maven build here:
https://cwiki.apache.org/confluence/display/qpid/qpid+java+build+how+to

Robbie