Bug 4247 - Clarify invite notification and options on /manage/invites

-- Rephrase link to /manage/invites in notifications
-- Rephrase Manage Invites title in several locations
-- Add explanatory text on /manage/invites and /community/manage
-- Rephrase various string on /manage/invites
-- Add text and list of links on success page
-- Add line-breaks
-- Downgrade subheaders to H2
-- Change UL to DL for community lists
-- Move dead string to deadphrases