Allow capping of ally's structures like mexes

It's not uncommon to end up with engineers near teammates' t2 and t3 mexes while the teammate might not have engineers nearby. Getting those engineers and eco to use fast would be great if an option was available to extend the capping functionality to allies. The options could be "Never", "Cap mexes and radars" and "Allow capping everything."
Of course the other respective capping options would have to be enabled too.

The capping allies' functionality would work the same as your own buildings - right-clicking/assisting them.

An argument might be made that capping storages (especially if they're not yours) with volatile mass fabs might be felt as griefing so that might be disallowed.