As an Owner, I can *easily* manage the broad permissions of my Space

Summary: At the moment, the system permits very fine-grained security. This is lovely in practice, but overkill in 90+% of cases, and harder to use than most users want. We need to boil it down to a few common patterns, and present the user with a simple radio-button choice that they pick at Space creation time, and can update later.

See this post and this poll for opinions on some of the details. Note especially the commentary, including ckd's suggestion about how this should work as a preference.