Introducing Layout objects, LayoutPlot & redesign of GridLayoutPlot

Redesign of the GridLayoutPlot and LayoutPlot now allows subplots
to be attached to a main view and placed in a GridLayout.
Added show_xlim and show_ylim options to Plot
Changed DataHistogram requiring inclusive bin edges to be defined
Stacks now update styles of views when added if they share ending
Added show_frame option to Plot
Added range and hist to SheetLayer and SheetStack objects
Removed colorbar from SheetViewPlot and added normalize_individually
Moved DataPlot above all other DataLayerPlots
DataCurves made square and disabled right and top axis spines
Redesigned DataHistogramPlot for use as colorbar
General cleanup in plots, fix to garbled hunks