Can change server to use as SA.

Choices are what's been the Forums' IP address for ages, or dev.forums if
available to the logged-in user, alongside the standard
forums.somethingawful.com. This required a couple changes in the HTTP client so
logging in and out works when switching servers.
Put "posts per day" back on post rate.

Fixes #194
Replace "Favorites" with "Private Messages" in "Launch Tab" setting
Add theme pickers for FYAD and Gas Chamber.

Closes #171
Don't pretend to return sent message.
Save a copy of sent PMs.
Reload posts view theme when theme setting changes.
PM list and view better update when settings change.
PMs need subjects or they're silently rejected on send.
Parse and show mod/admin stars for PMs.
Hide PM list for users without platinum.