Add STL Media Support

[Jeff Moe]

It would be nice to have STL support. STL is the most common format used by 3D Printers and is easily exportable from a wide variety of CAD programs (free and proprietary), such as OpenSCAD and FreeCAD.

Currently the largest site hosting STLs is thingiverse. The thingiverse site is closed, and the company that runs it recently released a proprietary printer that uses proprietary software. A free alternative would be most welcomed.

[Aeva]

Support for this should be added as a media type.

The workflow would be that a user submits a binary or ascii STL file or a textureless OBJ file, then mediagoblin verifies it and pushes the file to the public store. The model will appear in the gallery with a webgl preview and a download link. The thumbnail will be a simple icon indicating it is a 3D model. If blender is available on the server, and the option to use it is enabled, a high quality rendered image will be saved for use as the thumbnail image (and also to replace the webgl preview for browsers that do not support webgl).

I believe I can implement the non-blender part of that tonight.

[Christopher Allan Webber]

This is merged!