Move to centralised configuration file

This change enables the use of a single configuration
file to allow for configuration of database and
message queue at runtime, not compile.

This provides a base to enable configuration via
configuration management tools such as Chef and Puppet.

The configuration file is hard-coded to /etc/openrail/openrail.cfg
and is of a simple format:

db_name: <database_name>
db_user: <database_user>
db_pass: <database_password>
db_server: <database_server>
nr_user: <network_rail_username>
nr_pass: <network_rail_password>