Create and view performances

This feature turned out to be several:
*Create a performance
*View a performance
*View the date create and by whom
*Add multiple customers and multiple partners to a performance
*View all customers and partners associated with a performance
*View a list of all performances by customer

@amZotti, @MikeyMurph77 - please take a look
maybe you should make some methods on the performance model so that you don't have to do ```.to_formatted_s(:long)``` a thousand times - like how about ```formatted_start_date``` or something