[WIP] Add export of KML

This is work in progress. Status on FF/Pale Moon
### Export from Drawing dialog
- [x] Points (including sizes)
- [x] Polylines (including coloring)
- [x] Polygons (including coloring)
- [ ] Text -> does not work

### Export from measure dialog
- [ ] All
The same could be done for the gaImport service but that's another story:)