Multisig: create wrapper around set_threshold and set_weight

[K1-R1]

Motivation

Create a wrapper around the set_threshold and set_weight methods called set_threshold_and_weight to allow updates to the threshold and weighting values without disrupting the m of n dynamic in a given multisig.

For example; a multisig with 2 users that each have an approval weighting of 1, that requires unanimous agreement in order to execute a transaction, currently cannot have a third user with an approval weighting of 1 added without disrupting the unanimous agreement dynamic.
I.e. as the threshold cannot be updated to 3 first ( as that would be larger than the total approvals ), the third user would have to have their weighting set to 1 first, at which point only 2 out of 3 available approvals are required to execute a transaction.