Fix validation that twitter creds are present.

They are looked up as secrets which initialize to `None`, but the code
was checking for empty strings.

This, along with zulip#80, fixes zulip#81.

puppet: Move /var/lib/nagios_state creation to zulip::base.pp.

Previously, in Zulip voyager, the cron jobs would spew error emails
every time they ran, due to this directory not existing.

This also tightens the permissions for the folder and avoids needing
to create a nagios user for Zulip voyager; it should be writeable by
both root and the zulip user and world-readable (and thus readable by
the Nagios user on zulip.com systems).

Add description of Zulip at top of README.md.

Based on PR zulip#22 by GedLawrenson.

Update the puppet nginx file to match apache

this updates the nginx configuration file to match the installation documentation requirements and apache configuration file.

Use -O option to wget when fetching zxcvbn

Otherwise the downloaded zxcvbn.js also includes garbage we don't want

Use current working dir instead of /tmp

Hackishly install a correct version of python-django-guardian in prod…

… install.

(imported from commit 1027e05a1a9805a17fcb4b8dea2c2cf8cda280af)

email_mirror: Use internal_send_message instead of the API

Previously, the email mirror queue worker used the API bindings to send
messages to Zulip, as if it were any other API client.

This is inefficient since we're running the worker inside the Django
context on a machine with database access; we can instead just use the
internal message-sending functions we use elsewhere. This also resolves
potential issues with SSL certificates, etc. that might occur when we
were previously making a HTTPS connection.

(imported from commit 3f0d200eec66d926a8c6b3b33b825ac5d0edfe12)

Disable use_socket manually for CUSTOMER13

This was causing tracebacks during message sending

(imported from commit 9dde67f07934fe7a5aef7036340eebb7c6f6a97a)

Revert "Ensure server still gets narrow operators as tuples."

This reverts commit 64aced74012101f3bdbd3a4e6066b46ad8e1f4ea,
which was always intended as temporary code until we upgraded
the back end to support dictionary-style narrow operators.

(imported from commit b8d3a19f3aad3d9d6a26b9dcc07f502c55b18edd)