Consistent error handling

- [x] Server must return errors that have consistent format.
- [x] Unify way of handling with Throw and Callback errors.
- [x] Handle all errors. Now app can skip some errors, for example in PulsarDB.
It's just the matter of taste. I prefer to do it in before, because between test executions someone can alter the test database, so the first test will run on the dirty data. Also mocha can sometimes have problems with calling `after` according to visionmedia/mocha#1043. I know that we need `afterEach` which seems to be working but still.