Macros need __License__ strings

[chennes]

A quick look through the repo seems to indicate that there are many macros with licenses written at the top of their source code, but no __License__ variable set. The Addon Manager now processes the __License__ string, interpreting it as an SPDX ID, and optionally allows users to filter on the value. A missing string will be treated as an "All Rights Reserved" license, which is overly restrictive in many cases. Macros with more permissive licenses should have that variable set. I've fixed a few of them myself, but could use some help with the remainder.

[galou]

@chennes Thanks for fixing this. For information, the corrections were done with 3ba4cba, f280896, ac9ff46, a0e69e0 and c1f8410.