Trim export setting

[xChillax]

As it stands, when exporting your sprite sheets, the image will export with a huge empty space. This is really bad for optimization since it causes the image to be bigger than it needs to be in file size, hence causing the game to take longer to load it.

It would be nice to have a setting to trim the sprite sheet when exporting it. This setting should be enabled by default since there are no cons coming from this feature.