Add Meetup Everywhere ignore set.

Added to help out with a bunch of Meetup Everywhere jobs.

(cherry picked from commit 6e91c50d12169d98c8e6cb744a363da46ab9c29c)
bot: Experimental !a < FILE mode.

This is intended for archiving Meetup Everywhere sites.  Most of the
sites in Meetup Everywhere are very small; therefore, if we were to
spawn 6,000-ish jobs, there will be a lot of wasted effort in

1. managing multiple jobs
2. duplicate asset files

!a < FILE gets all sites in one set of WARCs and could end up being more
time- and space-efficient.

(cherry picked from commit cd49c7ae9bf083904823f1894ff73ac7a9560ee9)
bot: Don't process !a handler for !a < FILE.

(cherry picked from commit b8f2e654e85e2f501dbacfc0e7dfe5eab7770815)