[Graphics] Improve icon set

[Robert Szczepanek]

With regard to upcoming QGIS 3 [1], I want to ask your for opinions and 
proposals on updating current icon set.
As proposed by Markus, we will focus however not only on icons for QGIS, 
but consider also other OSGeo projects, like GRASS.
Please write your comments in *OSGeo Graphics* mailing list [2] or 
directly in GIS-icons issues [3].

This message is cross-posted, so please open new threads in Graphics ML.

regards
Robert Szczepanek

[1] https://lists.osgeo.org/pipermail/qgis-psc/2017-June/005387.html
[2] https://lists.osgeo.org/listinfo/graphics]
[3] https://github.com/Cracert/GIS-icons