Change-logs:

- Now preserve various parameters when the game is saved/loaded, i.e map's ambient, light's status/offset/color. Will add more in the future.

- Add a new parameters to lighting: Status. Control the status allow you to turn on/off the light anywhere you want without need to removing/adding the light repeatedly.

- Add a new parameters to shadow: Offset. Give you control over the shadow source cast position. The shadow offset will be addition with the light offset, i.e. if you set the light offset to 48 and shadow offset to 4, then the shadow source will be calculated at 52.

- Fulfilled all the default parameters. Now you can easily install the plugin to your project without having weird bug cause by the blank parameters. Also add error throwing when you don't have the image file needed.

- Fix minor bugs.