Add support for post_title and post_name orderby parameters. Add support for order parameters

Adds support using WP_Query's own `parse_orderby` method.

Provides defaults for both `orderby` and `order` if none are passed.

Adds test cases that should cover all added lines of code.

Currently just added `post_title` and `post_name` but other `orderby` parameters should be able to be added with much less work now.

@tlovett1 #review