Support svg icons

[Confectrician]

We should refactor our build tooling to allow svg graphics.

Thanks to the efforts of @ecdye we made some nice progress with the png logo sizes and some first svg logo tries.
Reference: #1557

From my researches the main preventing source for svg logos should be our build tooling (see final branch) and especially the process addons groovy script.
The script currently looks for png images exclusively, which should be extended to svg.

We also have to check for other locations, where a limitation could be configured. (e.g. the pom.xml file in the final branch.

cc @ghys

I think vuepress should be capable of using svg files instead of png ones.
But we maybe have to adapt the process docs ruby scripts too then.

Probably it would be a good idea to extend the frontmatter with dedicated icon information.