Visulization

I have updated the vtkView class, added error checks in .setters and fixed bugs that where crashing the objects. I have test on my system and it works.

Changes:

* For consistence: use C, F, E in stead of Cell, Face, Edge to indicate viewing properties. 

* .viewprop: dictionary, that set the view type and property. Example {'C': 0} to view cells and the 1st property array. 

* .limits: to cut off values below and above. No restriction to values other the they are floats. 

* .cmap: color map. Has to be matplotlib.cm.* made with flag bytes = True. 

* .range: color range. 

* Improved the example in **main**.

-- Originally a Bitbucket pull request by gkrosen