Move min_threads out of py into env; #1151

We need to be able to tweak this in heroku config, not requiring a
redeploy.
Bump version to 9.3.42
Bump version to 9.3.42-dev
fixed no method error showFeedback
Add an intermediate table for homepage queries

This addresses #659 by adding three new tables:

 - homepage_new_participants
 - homepage_top_givers
 - homepage_top_receivers

These are created as empty tables in schema.sql, and then in
configure-aspen.py, a daemon thread is started on server startup that
periodically runs the heavy queries needed to populate those tables. It
does so atomically in such a way that reads from the table are not
blocked while the table is being written to. The periodicity is
configurable with the UPDATE_HOMEPAGE_EVERY envvar (int seconds). The
queries in index.html are updated to use the new tables.
Merge pull request #1155 from gittip/issue659

Add an intermediate table for homepage queries
Bump version to 9.3.43
Bump version to 9.3.43-dev
Adding titles to community pages
Merge pull request #1154 from nika-m/payments_fixing_no_method_show_feedback

Fixed no method error showFeedback
Merge pull request #1160 from gittip/titles-for-communities

Adding titles to community pages
Pre-emptively escape page title

Haven't discovered a vector for this yet but it's stupid not to escape
this. Found this on #1156.
Merge pull request #1161 from gittip/escape-title

Pre-emptively escape page title
Bump version to 9.3.44
Bump version to 9.3.44-dev
Note ShareTribe on README