Created simple skeleton with panels: left, right, top, bottom, center.
Improved panel skeleton
Improved panel skeleton further, empty panels are now invisible (no border)
Fixed background size (did not reckon with borders of root panel)
TimeAxis starting to work again
Timeline repaints when orientation is changed
Added a horizontal and vertical background element
Moved grid lines of TimeAxis to the background panel
CurrentTime and CustomTime working again
A fix in the height of the vertical grid lines
ItemSet starts to work again
Introduced a forgroundVertical panel, positioned the dots of item boxes there
Fixed offset in zooming with scroll when using groups
Moved CurrentTime and CustomTime to the foreground panel
added dragNodes option. Renamed dragGraph option.
updated History
Merge remote-tracking branch 'origin/develop' into develop
minor bugfixes for git issues #157 #158 #159
Merge branch 'develop' into predefined_panels

Conflicts:
	src/timeline/Timeline.js
Merged from develop branch