Revert "tests: disable actual plotting in MATLAB"

This reverts commit 0f3346ebf2bca55d043a0e091a00913a5722fef6.
Add `figureVisible` parameter to ACID test

This allows to toggle figure visibility, which is cleaner and
faster in generation of the figures.

Do NOT set the global setting for this, as this will introduce unwanted
behavior in other scripts.
Fix test 15: do not create a figure in the test

Test functions should not create figures themselves
Skip colorbarLogPlot test when unsupported

On Octave and MATLAB R2014b, the logarithmic colorbars are
not documented and hence not supported. We should skip in those cases
Merge branch 'testVisible'