Changes module schemas to be returned by a model class method.

This is built off of the cyc-header PR #605 and should be pulled after it.  This has a companion PR in cycamore.

* Added schema method to model class.
* model schemas no longer need the wrapping `<element name="MyFacility">` tag - it is now auto-inserted by cyclus core.
* cyclus binary now has flags for dumping a specific module schema and the cyclus master schema (with all module schemas inserted into it).
* Moved remaining sim initialization code from model class into xml_file_loader.
* Housekeeping