Review DDS / PNG Approach

[aussig]

Currently, we copy both PNG and DDS files to the website and library builds.

This is probably no longer necessary, as X-Plane will prefer DDS unless texture compression is off, and even then it gives good results. However, we still need PNG for mobile 3D previews on the website.

So, once #62 is completed, perhaps the logic becomes this:

1. If we have a DDS available, we copy it and not the PNG to the library build.
2. If we only have a PNG, copy it to the library build.
3. Only copy the PNG to the AWS build.

To do this, we will need to ensure there are PNGs for every texture, including those that only have DDS versions at the moment.

If either DDS or PNG textures are missing, rather than both at the moment, this becomes a failure case.

Unfortunately we currently build a single library folder then sync the whole thing up to AWS. Will need to:

1. Create separate library and AWS build folders
2. Only copy one of DDS, PNG to library build folder
3. Only copy PNG to AWS build folder (will also need .obj, .fac, .for etc.)
4. Sync AWS build folder to AWS.