Update our project metadata tests to stand up their own projects, so
they don't trample all over each other anymore.
The fixes for this were more invasive than I had hoped they would be,
but the tests all pass now (when run sequentially) and there's no reason
for them not to pass when run in parallel.
Common metadata state is now stored
Optimistic locking support added to common_metadata
Revisions to keys in project metadata are now reflected in the project state
Wrote tests for project metadata (all pass)
Relaxed test conditions to work on projects with extra keys
Added documentation for project metadata
