Multi-Sig Cleanup

[dustinengle]

I believe this could be resolved with some UX improvements, doing some research I can see where the confusion came from.

1. There's currently no easy way to find a previously generated pay-to-multisig scripts, without knowledge of how P2MS works and it's format to allow a user to manually create it. It would be useful if the multisig dialogue could re-create the ScriptPubKey in addition to the error when creating a address already found inside the wallet. This was the root cause of our issue because I had lost the redeem key and couldn't generate it again to pass it on to @LyGhT1337 .

2. Being inquisitive, I went online to find a debug console command to try and force the wallet to generate the P2MS redeem again, and stumbled on createmultisig, not knowing much about the topic, this lead me to generating a P2SH redeem which I passed to Lyght. Given that we have the GUI in place, may we want to consider disabling the createmultisig command to prevent any user confusion in the future? Maybe not, but something to consider.

Originally posted by @KaneoHunter in #143 (comment)