Permissions - SMS - Add permission to use SMS

Currently, the permissions for SMS can only prevent Users from sending broadcast SMS to two or more people. They can send as many one-off SMS as they like.

We should have a way to prevent a user from using SMS entirely, just like we can prevent them from sending a single email using the "Can Send Email" permission. 

Please add a permission setting for "Can Send SMS" that would enable or disable sending a single SMS message.