Removing GroupSet references from Timeline
Some fixes in updating/deleting items
Merge branch 'develop' into itemset

Conflicts:
	src/timeline/component/ItemSet.js
Moved function getLabelsWidth
Removed console.logs from code
Merge branch 'develop' into itemset
Fixed changed ranges not being deletable
Merge branch 'develop' into itemset
Inserted some more group functionality to ItemSet
New Group starts working
Isolated calculation of visible items in function updateVisibleItems
Created a Group holding ungrouped items, for timelines not using groups
Added background and axis frame per group
Removed parameter `parent` from Item constructor
Some refactoring
Halfway large refactoring of ItemSet/GroupSet/Group
LabelSet working again
Fixed removing items
Fixed a positioning issue with ItemPoint
Fixes in updates from DataSets