Asynchronously re-read updated documents #257
Description
Motivation: current DB model is quite performant. All the data is read once on load, and then is only updated. Nevertheless, DB files could be updated from external sources (e.g. by external synchronization processes like Dropbox/Git/etc). Since changes in a DB file are not currently monitored, such scenario may lead to data loss.
Solution: we should implement a mechanism of checking "freshness" of DB files and provide some kind of "refreshing" when changed occur.