TN: create account: add optional multi-sig assign owner/other auths

[relativityboy]

As a developer of account alternate auth utilities on Steem, I want an easy api/ui to assign multiple different auths at different weights on account creation, so that I can create accounts and develop my apps more quickly on Steem.

AC

• api endpoint supports assigning up-to max number of alternate auths and auth types.
• ui on create account page supports setting the above auths, uses dropdowns for auth types.