CASC-200: Support client configuration from a properties file

This pull allows for a configuration properties file to load client settings. The location of the file can be retrieved via current means of providing settings (filter, ctx, jndi), and is tagged under the param name "configFile". A default location is specified at /etc/cas/client.properties

Existing configuration settings are kept. Pull contains tests to ensure order is preserved.

https://issues.jasig.org/browse/CASC-200