Query with ordered results

#### Design
The feature included in the current pull request allows ordered query by multiple fields for both mock and non-mock database model. However, it only works with the `Query Builder`, but does not support the basic `findBy...` methods.
- For non-mock database model: an `Order By` clause is generated and attached to the end of the SQL statement.
- For mock database model: since the mock model does not touch the database, the above strategy would not work; therefore, an unordered result set is first retrieved by the original query method call, then it is sorted by comparators and stored in a `List<T>`.

This feature should not interrupt any working use case of the current system. All the original test cases have not been changed. I tried to follow the existing design as much as possible. However, a few method calls were refactored to accommodate the changes.

===

#### Ordered query methods
- `asc()` and `desc()` - the `JackOrder` that can be passed into each order specification to allow ascending or descending sorting; `asc()` is the default order.
- `order()` - a query command that sort the result by ID.
- `orderBy[SpecificField]()` - a query command that sort the query by the specified field.
- `findWithOrder()` - a query command that completes the query builder, triggers the query and returns a `List<T>` of database models.

===

#### Examples
```Java
List<User> result;

// A simple ordered query that sort the result by ID ascendingly.
result = users.query().bio("Engineer").order().findWithOrder();
// The above query is equivalent to:
result = users.query().bio("Engineer").orderById(asc()).findWithOrder();

// A chained query that looks for users with 3 posts, and sort the result
//   first by ID descendingly, and then by the number of posts ascendingly
//  (which is the default order).
result = users.query().numPosts(3).order(desc()).orderByNumPosts().findWithOrder();
// The above query is equivalent to:
result = users.query().numPosts(3).orderById(desc()).orderByNumPosts(asc()).findWithOrder();
```

===

Please let me know if you have any problem using it, as well as any suggestions. Thanks for your time and attention.

LiRen Tu
2014.08.18


You want to make the change and use the Comparable class here actually