Reorganize conf; add test email server; add tests

Previously, the configuration loading was a bit scattered: `conf.json`
defined configuration, but these were munged and filtered by
`bin/unhangout-server` and `lib/unhangout-server.js`.  Some libraries
received this munged options object on init, but some did not, and had
to load options directly from `conf.json`, leading to some
inconsistencies.

To fix this, move all configuration loading into `lib/options.js`, which
all libraries should use to load configuration unless they have a very
good reason not to.  Remove all munged names -- names of configurable
options should be the same as those found in `conf.json` (including the
"UNHANGOUT_" prefix where present).

Add a test email server in bin/email-server.js, which can be used
for displaying emails on the console as well as maintaining an outbox
for use by unit tests.

Add tests for "Create an Unhangout" button and email handling.