Add Fallback icons
When running on GNOME, several icons are missing in it's default icon theme. For Pure Maps and OSM Scout Server, I have included required icons and configured them as a fallback.
That would require,
- adding icons to Neochat, as in https://github.com/rinigus/osmscout-server/tree/master/icons/fallback
- adding them into search path, as in https://github.com/rinigus/osmscout-server/blob/master/src/main.cpp#L183