Non-readability of widget Keyterms

[kermitt2]

The widget Keyterms become quickly unreadable, and the visualization goal is not reached.

See bellow, keyterms for organisation Inria - http://traces1.saclay.inria.fr/inria/organisation_dashboard.html?orgID=5

• colors are distorted/buggy in comparison to legend, see the orange of "Mathematial optimization" which becomes dirty green, so not possible to track visually keyterms

• far too much overlapping stuff/areas, impossible to distinguish keyterms

• density of publications in the recent years makes the old year keyterms too close to zero, so not visible

• the visualization is too much impacted by the growth of the number of publications, and the evolution of topics over time become unreadable/indiscernible

Suggestion: use normalised stacked bar, see #45
experiment with steamgraph maybe