multisite licenses changes, move logic to license manager on a per-plugi...

...n basis

This uses the `feature/network-licenses` branch of the License Manager repository.

https://github.com/Yoast/License-Manager/commit/72737388684f885e2d02a1eb46ec3c66e69b3f04

https://github.com/Yoast/License-Manager/tree/feature/network-licenses