First attempt at error handling in the controller.

Doesn't really do anything but allows the use of a custom error handler. Currently there is a problem because the table columns are showing depending on which are in the selected columns list, which currently gets filled regardless of whether the API request was successful or not.
Tidied up some debugging leftovers.
Using error handler for all work package service requests.
Fix typo
Add service error handler to the promise returned by the callback
Merge pull request #968 from opf/feature/ui-component-table-widgets-robust-loading

Feature/ui component table widgets robust loading