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 vertical position of timeline chart elements in aggregation

fixes #4889
Fix label positions and string truncation of aggregated planning elements within timelines chart
Avoid error when second level grouping is applied but first level grouping is not

Conflicts:
	app/assets/javascripts/timelines.js
Decompile second level grouping adjustments, preserve at least one reporting to root

Disclaimer: The specification is kind of weird
Disable deactivated custom field columns before timeline rendering

Conflicts:
	app/assets/javascripts/timelines.js
	app/assets/javascripts/timelines/TimelineLoader.js
	app/assets/javascripts/timelines/model/CustomFields.js
Refactor custom field step
Fix timeline custom field filters

The timeline id is needed by the api/planning_elements_controller to correctly initialize the query
Show filter field set if a boolean custom field filter has been applied
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
Sorting now taking place in API calls not page reloads.
removed comment.
Rearrange reload of query results when the sortation is changed
Add remark
Merge pull request #972 from opf/feature/ui-component-table-widgets-column-sorting

Feature/ui component table widgets column sorting
WIP Added a directive for table pagination.

Currently only supports per_page and not page number.