Membership; User.login -> User.name; much more!

- Users may have a single home repo.
- Repos do not all have owners; only when they are
  a home repo.
Tweak some __repr__ and logging
Squashed 'lib/PyHAML/' content from commit e44df1f

git-subtree-dir: lib/PyHAML
git-subtree-split: e44df1f386145e52b71c028cef50ba08e868858a
Merge commit 'fda5d525fc2cff280a1c5f27259d5b9ccb8500a0' as 'lib/PyHAML'
Mixin calling can have dots
User homes are groups
Membership removal cascades
adducer -> user
`rebuild` to test
Tweak group/repo layouts