A mathematical morphology framework for Imglib2.

This PR ships a small mathematical morphology framework for Imglib2.

Rather than documenting what it does and how to use it, I put documentation and benchmarks on [Imglib2 wiki](http://fiji.sc/Imglib2_Morphological_Operations).

Though mathematical morphology extends far beyond what is contained in this PR, I wish to subject it to the team scrutiny early. 

For instance, this PR contains several calls to deprecated classes, I did not know how to workaround.