249: Remove SKIP workflow code and fix unit tests, API

[tngreene]

SKIP workflow was a bad idea, now canceled. We need to remove the code (small) and change some of the early unit tests that were counting on it to use REGULAR or BULK (medium).

• Remove SKIP related code
• Change early tests that were counting on it to use REGULAR or BULK
• Change APIs so they can assume there will always be a root object, code clean up (this point especially important)

See #381 for where this came from

[tngreene]

Should the policy be "convert as many things as possible, unless dependent on Root Object?"

After seeing the amount of work sometimes not currently under a root object as a "rough draft, don't export" solution it would be really terrible to not have this work converted as well.

Hundreds of mesh's and material's unsplit, and lights unconverted for no reason that the user may someday want again. Texture conversion absolutely needs to start from the root down, but the others I see no reason why we shouldn't be going by per datablock.