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
or if you basically only ever want to read the start date as a pretty-format string you should change the method to return that