Overhaul session handling; pure URL-based sessions are subject to
copy-paste session-stealing. Convert to cookie-based session tracking
instead. This also provides bonuses in terms of inlinks from other
utilities or copy-paste links.
While session-handling was in pieces, add "pick-up-where-I-left-off"
login handling so that logins don't always end up only on the initial
domain list. This is especially handy for copy-paste links.