Add trivial EnsureFounder verifier to society

[gavofyork]

Needed for sensible usage of the pallet.

[shawntabrizi]

You could also consider adding:

ensure!(Self::founder() != Some(m.clone()), Error::<T, I>::Founder);

To the remove_member function, which would make it so that this founder cannot be suspended/removed from society.

Also this adds 1 storage read to the found extrinsic.

EDIT: Also, so I understand, this origin will likely be used for the SuspensionJudgementOrigin, but the FounderOrigin in the trait config will need to be some hard-coded address right?

Would it make sense to update the name then to BootstrapOrigin?