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
Cherrypicked from branch fix/remove_layout_tables_4112

Implemented changes to the work packges index view which are now in the work packages options angular template.
Show filter field set if a boolean custom field filter has been applied
Fix typo
Cherrypicked from branch fix/missing_labels_4118.

Accessibilty for timelines zoom select and outlines select.
Add service error handler to the promise returned by the callback
Cherrypicked from branch fix/icon_link_table_comprehensibility.

Timelines add work package icon has span with hidden text.
Fixed typo in locale names in template.
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.