Enhance license actions

[cssjoe]

After manually entering a license key, the "Verify license key" button says "License key is correct and can be activated now." when it is valid. The user must then save the settings for it to be applied. We should save the verified key on success and inform the user that the license has been applied.
If the verify button is clicked again after a license has been applied, we should check if the key is being changed and run the process above or inform the user that the license has already been applied.