fixed crash when the scene view is not visible
camera is moved not in one frame during look at command
visualize what windows are visible - closes #308
save/load custom layouts
each stroke can be undone when paiting terrain's height
raycast only terrain when paiting - closes #276
color input in the property view shows the selected color
reviewed code - missing reference added
Merge pull request #310 from nem0/editor_improvements

Editor improvements