Move from GPLv3 to LGPLv3 or later

Skyline has been licensed with GPLv3 but as we want to look into optional ads in the future, and that would require linking AdMob SDKs which are proprietary. So, we decided to move to LGPLv3 so we could keep that option open as a revenue stream. 

We've gathered consent from all contributors for the license change:
* PixelyIon - https://github.com/PixelyIon (Commit Author)
* Zephyren25 - https://github.com/zephyren25
* ByLaws - https://github.com/bylaws
* IvarWithoutBones - https://github.com/IvarWithoutBones
* Cyuubi - https://github.com/Cyuubi
* greggamesplayer - https://github.com/greggameplayer

app/src/main/cpp/skyline/services/am/IApplicationProxyService.h

@@ -1,3 +1,6 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// Copyright © 2020 Skyline Team and Contributors (https://github.com/skyline-emu/)
+
 #pragma once
 
 #include <services/base_service.h>