Provide option to set "Generate a unique license key" for each version#293

I release my scripts usually as trial, single seat and site license. If i enable this setting for a product its for all versions, and the person that downloads the trial version will receive also a serial number, which is not desirable.

At the moment i can either cover this case during the activation code on my end or duplicate the product page just for the trial version and disable this features there.

Hope you will consider this in the future !