N3GOV-40: Elect the Guardian Multisig

We now have two guardian candidacies (Santi and Raymond):

https://forum.nation3.org/t/submission-of-candidacy-santiago-siri/906

https://forum.nation3.org/t/submission-of-candidacy-raymond-chen/888

This proposal would elect them as signatories in the Guardian Multisig, which would oversee the high-level output of guilds and dispute their agreements with the DAO if they aren't delivering.

This proposal also:

• Renames the Guardian Guild to Guardian Multisig: The word guild can be confusing as it can mean a loosely delimited group of people — which isn't the case here.
• Delimits the responsibilities of the Guardian Multisig to disputing the agreements with guilds, not other administrative tasks.
• Renames the Meta Guild to Ops Multisig: Same as with the previous rename, and it also reduces the ambiguity that the word meta produces.

PRs at https://github.com/nation3/law/pull/5/files and https://github.com/nation3/gov-proposals/pull/58/files