LU decomposition: refactor API and remove XXXwithNaiveBLAS class/object

Comment out method "solve" in Matrix until we have finished with
the reorganisation.
Less verbose printouts and add one test case for size > 32
Recursive LU: use unblocked LU when panel width below some threshold

Before the algorithm would recurse all the way to a single column
Benchmark LU decomposition against jblas and netlib-java
Reinstate Matrix#solve