SolverBenchmark added

A class itself and a unittest for it.

Bugfix in multiarray. Formatting issues in multi_array.h fixed.
Multitable improvement (now not using lexical_cast when printing
axis- and tick-labekls).

Change-Id: Ibf5a297648a9df2aac8fe7d912bca04657313a0f
Merge "SolverBenchmark added"