get SVG "icons" for admonition / new / updated

[DougBurke]

Can we use SVG rather than PNG for some of our icons to better match screen / resolutions?

[DougBurke]

One source for the admonition icons is

https://github.com/neo4j/doctools/tree/master/src/main/resources/images/icons/admon

although the look is different.

[DougBurke]

There are also versions at

https://github.com/docbook/xslt20-resources/tree/master/base/img