check on proper citing/licensing of employed matplotlib related sections

[Joern Ungermann]

Our modification of the navbar uses partially copied code from the matplotlib implementation.

Review the license/attribution, and possibly simplify the implementation.

The code should also be aligned closer to the current implementation as the discrepancies caused the recent deprecation related program crashes

[Reimar Bauer]

the citing of the license needs to be done where the code is

[Reimar Bauer]

Added a section w.r.t. matplotlib to the LICENSE file.

Fix issue #438

→ <<cset 077059bb6a97>>