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.
The location for System-wide and User-only installation depend on Windows-managed locations, which means that they will never require a user to select the correct location. Therefore it is best to hide the page in all modes except for Portable, which should still offer a path to extract to.
Thanks to the PR by @abcdw (https://github.com/obsproject/obs-studio/pull/4067) we can support 'local user' installations. These will allow end users to install StreamFX without requiring Administrator rights, or learning how to use OBS Studio in portable mode.
With OBS Studio 0.15.0 came a better location for plugins to install to, which solves many of the current issues. While this location still requires Administrator rights to write to, it is a much safer location than writing directly into the OBS Studio installation directory.
