Reuse the IResource instance.

The IResource is stateless so it is OK to reuse it.

Optimize imports
Minor optimizations to the way the /json response is created.

* reuse the IResource - it is stateless so it can be reused thread safely
* use Content-Length response header
No need to initialize IdentifierLoadAccess for each record
Optimize imports
Don't log WARN

As prescribed at http://www.techempower.com/benchmarks/#section=code do as less logging as possible
Merge branch 'master' into wicket-optimizations
Merge branch 'wicket-optimizations' of https://github.com/martin-g/FrameworkBenchmarks into PR647

Conflicts:
	wicket/src/main/java/hellowicket/HelloJsonResponse.java