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.
'Perspective' and 'Orthographic' work great if you know what the parameters were to generate the exact object position, but what if you don't know them? That is where 'Corner Pin' comes in! With it you can specify the exact location of every corner down to the micro-pixel, instead of fiddling with parameters.
Fixes#565
