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.
While the previous approach of a static thread pool worked, it was sub-optimal in its resource usage. Many of the threads would never see a single task, and simply permanently sleep. This seems like a good idea, except that sleeping threads still end up in the scheduler, and thus waste a tiny amount of resources.
It is better to instead dynamically spawn threads when needed and only keeping the bare minimum around all the time. These dynamically spawned threads are also explicitly set to background priority which further reduces scheduling overhead. Finally optimizing the memory layout to prevent unwanted false sharing should also keep sporadic wake ups at a minimum.
This new model should be able to handle many more tasks than ever before, but is still not as optimal as it could be.
To ensure better stability of future releases, we need to adopt multiple stages in the release cycle. As we already label Alpha, Beta, Candidate and Stable differently, simply adopting this classification system already does everything for us. This also allows us to maintain compatibility with the existing system, while offering something new entirely.
Implements a manual and automatic update checker with support for both release and testing update channels, allowing users to stay as up to date as possible. It is fully compliant with privacy regulations around the world, as it stays completely silent and inactive until the user gives the Ok to connect to GitHub for the latest releases.
