Move viscript/msg to new repo

[gz-c]

viscript/msg is imported by other apps (skywire, skycoin), causing import loops which mess with dependency vendoring. However, viscript/msg still imports skycoin/cipher

viscript/mesh or viscript/mesh/run_mesh maybe need to be moved to a new repo too. This package imports skywire and appears to be a command and not a library method.

[gz-c]

I don't know if all of msg has to be moved, or only part of it