Zotero.DB updates

- Fix ES5 generator in executeFile()
- Remove deferred in executeAsyncStatement()
- Remove obsolete properties and wait level check
Allow StopIteration in queryAsync() to cancel query

And catch other errors and throw StopIteration so that they stop the
search. (Non-StopIteration errors in onRow don't stop Sqlite.jsm
queries. We were logging them but then re-throwing them, which didn't do
anything.)
Closes #527, Asyncify autocomplete
Use 'Zotero' object instead of this._zotero in autocomplete