Create license file for distribution with dist

[prushforth]

Since everything in dist is being slightly obfuscated / compressed by the build, we must generate a license file in that directory and distribute a copy of all the licenses that we depend on.

The Leaflet library
Fullscreen control
Geolocation button
proj4leaflet
proj4
Fullscreen control
ContextMenu
Web-Map-Custom-Element
Crosshair

Other tbd