M-of-n phase 1

Even though multi-sign is not finished (it's missing fees and reserves, metadata, and some validation) a significant amount of work has accumulated.  Yana, Nik, and I feel it may be a good idea to go ahead and give the work-to-date a serious review and hopefully get this phase of the work into develop.

I've attempted to disable access to multi-sign features using some carefully placed #ifdefs in the last commit.

@JoelKatz @nbougalis @vinniefalco