Dialog popup for multi-host-at-same-location, also includes new marker icons

This has a number of map improvements, including 

#95: Open a dialog instead of leaving map when multi-host single-location marker is clicked
#94: Use a new icon for map pointer

And it has a bit of history trying to diddle the look of the map.

It won't apply until after the other current outstanding PRs, mostly #108, but I'll be happy to rebase it quickly when those go in if it doesn't apply at that point.