Added support for Tiberian Sun/Red Alert 2 SHP format

Thanks to @katzsmile who added this to his SHPViewer fork. Tested with #3192, but it will also work in-game: http://www.moddb.com/mods/cnc-reimage/videos/open-ra-engine-shpts-format-demo

![aE5x3Xx](https://f.cloud.github.com/assets/756669/439498/c23c2b66-b0e4-11e2-9f2b-82dfb77fc67e.png)

Note: since Tiberian Sun the shadows are separated and many units also make use of overlays so this requires #2211 when we do a ts mod.