Tweaks to prevent memory leaks (it doesn not fix the memory leak)

* Async operations wait for process.nextTick() as it is recommended by Node's
  documentation.
* Disable jsdom features.
* Close DOM window after it is used in BillImporter.
Fixes #4: implement directory tree balance strategy in FileSystemStorer.
Merge remote-tracking branch 'origin/master' into develop
Added references to votes.
Replaced jsdom by cheerio to fix a huge memory leak and improve performance.

* Improved data consistence.
* Added text url to bills.
Fixed bug in vote importer.

* Votes were replaced in each motion page, now the full list of votes are
available.
Update README.
Update version up to 1.3.0