R1:3c30ea41f11b

Enable multiple web sessions

Summary:
Conduit already has multiple-session code, just move it to the main
establishSession() method and set a web session limit larger than 1.

NOTE: This will log everyone out since we no longer look for the "web" session,
only for "web-1", "web-2", ..., etc. Presumably this doesn't matter.

Test Plan:
Applied patch, was logged out. Logged in in Safari. Verified I was issued
"web-1". Logged in in Firefox. Verified I was issued "web-2".

Kept logging in and out until I got…