Updated Cheddar to allow for PersistenceException handling when initialising database write actions

+ Also included in this PR is the addition of a read/connect timeout for HttpClient.
The application code would look like this:

```java
final PersistenceExceptionHandler<BadException> handler = new PersistenceExceptionHandler<BadException>() {

  @Override
  public void handle(final ItemConstraintViolationException e) {
    // stuff
  }

};
```

The "handle" method is part of the interface for the PersistenceExceptionHandler