refactor layouting code

[wirew0rm]

goals/current problems

• reduce hierarchy depth
  • prevent layout/rendering loops caused by resizing during rendering
• increase flexibility (allowing e.g. 3D axes/plots)
• some size computations are currently performed in the render step (mainly computation of axis labels and size)
• tick computations are performed in the rendering step of the axes, but the grid is drawn before the axis (#410)
• correctness: currently the axes and charts rendered are not always consistent in every render loop, which is inconvenient for exporting images of the rendered chart => after the render step is completed, the display should be consistent. (There might be things like clipped/overlapping text until the next repaint if it is not preventable, but the data should be correct.)

current state

scenegraph

implementation

• use a single canvas as the root element to also allow for 3D plots and allow more flexible axis types?
  • most chart elements already use a canvas and some sort of coordinate transform
  • would need to implement custom mouse event handling
  • would decrease the usefulness of common javafx tooling?
  • extensibility with standard controls?
• use a custom layouting container which computes the positions of all chart elements in a flat hierarchy
• first compute data ranges from renderers in layout step, then compute axes ticks, then render charts and axes

... to be extended/discussed further