Updating resource checker to support material's mainTextures that aren't included at build time

The resource checker was only checking a game object's editor dependencies to get the associated objects. If you download a texture using WWW or otherwise create one at run time, it wasn't showing up. It now will, so long as it is the mainTexture of the  material.
Merge pull request #7 from jtothebell/master

Updating resource checker to support material's mainTextures that aren't...