Adds dbmail migration expire_unsent_emails

Adds a migration to expire old, unsent messages, so that the code
changes from 6e350a3735 do not cause out-of-date emails to be sent.
Adds migration constraint to dbmail cronmail

Requires that the expire_unsent_emails migration has run before allowing
cronmail to process or send emails.
Converts ZipCode initial_data fixture to migration
Adds script to manually install certain packages

In particular, it has been problematic to install the correct versions
of node and node-less. Fixes this problem by installing them manually
from .deb files available online.
Bumps Django to version 1.4.10
Consolidates dependency installation in update_deps.sh
Fixes check for nodejs
Add nodejs dependencies to packages_base.txt
Move installation of pesky packages to packages_base_manual_install.sh
Move libc-ares2 and libev4 to packages_base.txt; shrink manual install code
Rely on apt to install twill since there was trouble installing with pip
Merge pull request #953 from learning-unlimited/deploy-fixes

Deploy fixes