To make it even more obvious that by default the permissions to check
aren't taken from the full method provided, we add a new flag that does
that on request.
This commit removes the usage of the standby nodes and uses
`CreateSimpleNetwork` when applicable. Also introduces a helper method
`NewNodeWithCoins` to quickly start a node with funds.
We've only ever made macaroons with the v2 versions, so we should
explicitly reject those that aren't actually v2. We add a basic test
along the way, and also add a similar check for the version encoded in
the macaroon ID.
