The license was renamed GPL-license.txt => license/GPL-2.0txt in 0434efa09ddc451.
Although the renaming made all the license files consistent, we are better off
not updating the copyright file in Blender. Instead we can live with some mild
inconsistency in the license names.
For the final builds instead of leaving all the license files in the main
folder, we move them to a "license" folder.
Also, adding more licenses here (MIT, Apache, ...).
Differential Revision: https://developer.blender.org/D8999