Open-source licensing changes

As from today’s new version 2.1.1, I’ve made a couple of changes to the juce licensing agreements:

The juce_core module will now be available under a permissive ISC license - that means that everyone is free to use that module commercially and to link it with any other code without needing a commercial license. (Thanks to Vinnie for sponsoring this change!) Hopefully this’ll attract some interest from server/command-line writers for whom juce’s core classes could be useful.

All the other modules are going to stay under the normal GPL/commercial system, but I’ve tweaked it slightly to also allow them to be used under GPLv3 or the AGPLv3. I don’t think these changes will affect very many people, but I’ve had requests for this, as it can be a headache to create open-source projects that combine libraries under different versions of the GPL.