Consider how to document and manage OSS vs proprietary taps

It came up in discussion about how people might want to use the hub for proprietary and unlisted use cases. The spec and the base design of the SingerHub should be built thinking about this at the start.

I'd estimate the following % for each type:

Code-type	Listed	Unlisted
OSS	90%	<1%
Proprietary	5%	<5%

We're going to focus most of our effort on the open source community, but will build will related use cases in mind.