Use in multiple plugins

[Andy Fragen]

From @mgibbs189

If this gets used by multiple plugins, there will need to be a way for each plugin to modify $config. Maybe something like:

$config = apply_filters( 'wpid_register_dependencies', $config );

Multiple plugins would each have their own wp-dependencies.json files. I think I've designed the class so that inclusion in more than one active plugin will be gracefully handled.

[Andy Fragen]

1b4c5d8 should take care of this.

Contents of wp-dependencies.json now passed into class instantiation.