[plottools] Rename or merge into cvtools

In 974daf8b we added plottools.py containing interactive plot and imshow functions for Analytics 3 and Systems 2 as Colab does not support %matplotlib notebook.

The name plottools may be insufficiently descriptive - something like interactive_plots may be more appropriate. Alternatively, in Core labs we already have ipynb_show_image and related functions. If it makes sense for plottools's imshow and plot to be a part of that file we should move them there.

Alternatively we may decide that plottools should stay as it is.