James Westman authored Oct 13, 2021 and Marcus Lundblad committed Nov 01, 2021

Removed the {append|prepend|remove}_map_source methods from
ShumateLicense and replaced them with a `map` property. The license
monitors changes to the map layers through a new `layers-changed`
signal and updates the license text automatically.

This also required adding `license` and `license-uri` properties to
ShumateLayer. Currently only ShumateMapLayer implements them and they
are taken from the map source.