Fixes several files incorrectly stated a different license from the actual project, as well as the copyright headers included in all files. This change has no effect on the licensing terms, it should clear up a bit of confusion by contributors. Plus the files get a bit smaller, and we have less duplicated information across the entire project.
Overall the project is GPLv2 if not built with Qt, and GPLv3 if it is built with Qt. There are no parts licensed under a different license, all have been adapted from other compatible licenses into GPLv2 or GPLv3.
With this, GCC 8 and above should now be able to compile the project both in obs-studio and as a standalone install. Some features are currently still not fully supported and require extra work, but the majority of things are supported and work out of the box. Exact feature parity can be looked up here on the wiki: https://github.com/Xaymar/obs-StreamFX/wiki/Platform-Feature-Parity
Related: #119#98#30
