log cases where node plugin defines an invalid nodeEditorClassName
test if CG context is nil (Apple recommendation)
assert when plugin node property name does not exist
improved CCNode description
added Sprite Kit Node plugins: label, sprite, sprite with color
fix crash when trying to "Save As" due to deallocated SavePanelLimiter
more tests with SK node plugins
Merge branch 'refs/heads/develop' into convert-reader-to-SK
Merge branch 'refs/heads/convert-reader-to-SK' into spritekit-node-plugins
sprite kit nodes work with reader (wip)
SB internal reader: skip nodes with missing plugin instead of asserting/crashing
fixed label node
fix color sprite opacity/alpha (workaround)