Allow more than 1 kml to be loaded at once

[Shawn Honomichl]

Would be a nice feature to be able to load more than 1 kml file at a time. Having multiple features in the same kml is a suitable workaround, but allowing more than 1 kml loaded at once would be nice.

[Reimar Bauer]

Done by https://bitbucket.org/wxmetvis/mss/commits/13b0f85e6604a17f7ab58847cecb8b98055af64b