[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

### Troubles
- [ ] Getting it to download on IE browsers
- [ ] Naming the file (now it's strange name)

### Refs
http://stackoverflow.com/questions/283956/is-there-any-way-to-specify-a-suggested-filename-when-using-data-uri
http://stackoverflow.com/questions/3749231/download-file-using-javascript-jquery
http://johnculviner.com/jquery-file-download-plugin-for-ajax-like-feature-rich-file-downloads/
http://stackoverflow.com/questions/7763505/is-it-possible-to-initiate-a-download-prompt-in-browser-for-recognized-mime-type

I have something that should be ok for encoding.

Downloading a JS generated blob as file is another matter cross-browser. Terrible...