Add license information to all files, re-update author list

[andersx]

• Everything should be explicitly MIT licensed.
• Additionally, some co-authors seem to have vanished in an earlier commit: https://github.com/qmlcode/qml/commit/8f16e47ad53bc5697263d24c6d4dcc5c8085db21#diff-04c6e90faac2675aa89e2176d2eec7d8