Improve SVG Import

[rosmord]

The homemade JSesh library for SVG import is small and efficient, but doesn't cover the whole standard. When I decided to use my own code, the reason was :

• I wanted to keep JSesh as small as possible ;
• including external libraries was complex at the time.

With maven or, one day, gradle, the second point is not a problem. As to the first, we are in 2021.