Adds 2 new permissions related to bulk user registration and bulk channel creation.  Permissions are assigned
admin role.

The nimble:restivus package, used by REST api, does not support alanning:roles with 'groups'.  It doesn't even
use the alanning:roles API to check for roles.  As a workaround, I removed restivus's rolesRequired check from
the bulk api methods and added Rocketchat.authz.hasPermission checks.

Update message pinning to show up on the tab list with a few options to allow/disallow it and whether to allow anyone to pin messages

This change also alters how edits are displayed both for sequential
and non-sequential messages.

See #1357

This comes in the form of the user's avatar, along with a hover
title that shows username and edit time. As a side note, this
requires us to start saving 'editBy' id as part of message updates.

This has been tested with all 4 of the current avatar methods.

fixes #824

Added user method for searching users from same domain

Note that this also makes a minor tweak to scope of "if description"
check in admin.html, that is more correct.

This change also swaps out the settings group display from <h3>
to <p> for a better look and feel.