Configurable charts fixes

make them work with datatables ajax requests
fix crashing null error if an x-value was empty
This will always evaluate to true because `self.extraCallbacks` defaults to an empty list, which evaluates to true in JavaScript. Either use `self.extraCallbacks.length` or change
`self.extraCallbacks = options.extraCallbacks || [];`
 to 
`self.extraCallbacks = options.extraCallbacks;`