Build a mechanism in Mir to allow our YAML configuration to be the primary configuration from which boost args are parsed

[mattkae]

How?

• We should add a new method in Mir called std::map mo::DefaultConfiguration::parse_custom(...) which will hook up to miral
• With this, we can supply a custom function that will return a map of options that will reach out into the yaml file
• In this way, we will circumnavigate the restriction of using Mir's config file