Bug fixes

• Improve directional light shadow resolution by rendering only the shadow texture for the scene instead of the entire light radius.
• Keep the directional light position at the original x,y coordinates to allow more flexibility in displaying directional lighting that is meant to be overhead on a map. This also gives more options for animating directional lights. Note that directional lights can be set to 0 bright radius if you don't want the bright circle on the canvas.
• Set elevation angle of the directional light based on only the scene rectangle, which should fix issues with changing to the padding %. Closes issue #68.
• Fix handling of door updates so the shadows properly update when opening/closing doors. Closes issue #71.
• Fix handling of light position updates so that shadows properly update for threshold walls when the light is dragged. Closes issue #67.