As of v0.2.0, GTK Layer shell is licensed under LGPL v3

while most of the individual source files are explicitly licensed under MIT, some generated files and the project as a whole is LGPL. This change was made to allow copying in code from GTK.

EDIT: More specifically, LGPL v3.0 or any later version

Changelog

• Relicense to LGPL v3
• Fix long standing issue with popup grabs
• Fix potential compatibility issues between GTK versions with gtk-priv headers
• Add GitHub Actions CI (just building and license check for now)
• Add script to check that are files are licensed correctly
• Use layer_surface->set_layer instead of remapping (when available) (thanks @alebastr)