Add settings module and read JSON

The Mo'Astro settings are, by default, located at ~/.moastro.json.
Add locate_server function to settings
Add dbtools.make_connection() function

make_connection is a pymongo Connection factory. It allows connections
to made either with direct specification of host URL and port, *or*, by
naming the server into the ~/.mongo.json configuration file.
imagelog and twomass use new connection factory.

ImageLog, MEFIngester and PSC classes now accept server keyword
arguments to resolve server names into URLs/ports and ultimately handle
the pymongo connection.
Remove old auth prototype module
Add settings api to docs
Test for settings.py

I've tried to add an example moastro.json file to isolate testing of
settings file parsing. However, I cannot seem to read that
data/example_moastro.json file during a test (the test runs the code
from a temporary directory). In the meantime I test against a
locally-install ~/.moastro.json file, but obviously this should be
fixed.

Added utils/pkgdata.py module to support reading package data.