Consider nesting Broadcast Messages and Targeted Messages under one nav item

The following discussion from !184959 (merged) should be addressed:

• @tyleramos started a discussion: (+4 comments)

  Question (non-blocking): This is more of a UX questions, but I'm just curious if we considered having Broadcast Messages and Targeted Messages nested under one nav menu item for "Messages"? Not a big deal, but they seem related enough, and even share the same nav menu icon, that it might make sense organizationally.