Refactor: move 'join_url' from abd to phl

Move the 'join_url' function from abdweb_arcydcontent to phlurl_request
so it can be re-used.

Test Plan: $ ./precommit.sh
Arcyd: better dashbd, big cycle timer, move stats

Improve the Arcyd dashboard by moving the stats down the page and making
the cycle timer more prominent.

Test Plan:
$ ./precommit.sh

$ ./testbed/arcyd/status_html_testbed.sh
- inspect dashboard in various states