Linear image on non-linear axis.

Employing a trick to get rid of the warning when using imshow() on
non-linear axis. The results are identical but I guess more correct and
no more warning is raised. See #748.
Replacing imshow() with proper logarithmic plotting.
Replacing TFMisfit plotting with proper logscale plotting.
Ensure some counts are really integers.
Force plotted trace type to be float.