- Add an 'exclusive' option to transactions that causes them to block other
transactions and wait for other transactions to finish before starting,
instead of nesting
- Resolve Zotero.DB.waitForTransaction() promise before returning from
executeTransaction()
- A side effect of the above: wait for a newly created item to be selected in
the middle pane and rendered in the right-hand pane before returning from
executeTransaction()
- Don't save items multiple times when adding/removing a non-final creator in
the Info pane
- Use a simpler, non-recursive method for focusing the next field in the Info
pane; this prevents "too much recursion" errors if something causes the
right-hand pane not to be rendered when expected
