Refactor Requirement#list_requirement_admins

[squidgetx]

This is just a nightmare of bad practice (some of it is admittedly my fault).

• Separate the backed part of the task (belongs in model) from frontend task (belongs in view and view helpers)
• Adjust spec accordingly

[orenyk]

Ha, I had this nagging feeling in the back of my mind that the whole method was really weirdly set up, so I'm glad it wasn't just me.