Accept json config files on the command line.

Any arguments given when starting the app are treated as json files
containing configuration that should override the builtin default
configuration.
Pull kibana proxying config out into separate module

Trying to make app.js really short and easy to read.
Authentication libs are optional; change syntax for specifying auth

This allows for configuring arbitrary auth providers by specifying it in
the new `authenticators` key of the configuration.

Bump version to 2.0 to indicate the breaking change.
Working on pam authentication

This kinda works but isn't very well tested; it also doesn't seem to be
using the session to prevent reauthentication over and over again.