[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

Yes we use it for display of cached tiles but run into encoding problems with this function on mac and ie.
FileReader is the best but this damn IE9 doesn't have it. 

May we can remove this functionnailty for IE9 because we don't have the import local file functionnality.