Adjusting code to slightly different backend and ajax.
Merge branch 'master' into cleaning-up

Conflicts:
	bin/example_server.dart
	pubspec.yaml
Small modifications (comments, DiffNotPossibleException).
Merge branch 'cleaning-up' into concurrency-issues

Conflicts:
	bin/example_server.dart
	pubspec.yaml
MongoProvider refactoring.
Fixed bug: selector overriding its key-val pairs.
Obtaining data and version using version->data->version approach.