Add Details Metabox to Testimonials

I would like to see a details box to save extra information regarding Testimonials. I suggest recreating the fields that exist in the Testimonials by WooThemes plugin.

I have the working code in this gist:
https://gist.github.com/bhubbard/4006b310421bb9cfb310a6442598ad37

Just throw that code in the bottom of modules/custom-post-types/testimonial.php or it can be in another file if desired.

Start with modules/custom-post-types/testimonial.php and review the linked gist for the proposed fields and metabox behavior. Add the details metabox for Testimonials, using another file only if appropriate, and verify that the extra testimonial information can be saved and displayed in the editor.

Written by the indexing model from the issue text.