Used Flask-RESTful for API

Closes #162
Good question. For such cases Flask-RESTful has ```fields.Nested```. For example:

``` python
class A(ndb.Model):
  b = ndb.FloatProperty(default=12.12)
  bb = ndb.IntegerProperty(default=12)
  bbb = ndb.StringProperty(default='bbb')

class Config(model.Base, model.ConfigAuth):
  ...
  test_a = ndb.StructuredProperty(A)
  def _pre_put_hook(self):
    self.test_a = A()

A_FIELDS = {
  'b': fields.Float,
  'bb': fields.Integer,
  'bbb': fields.String,
}


CONFIG_FIELDS = {
  ...
  'test_a': fields.Nested(A_FIELDS)
}
```
...
![screen shot 2015-01-01 at 21 56 59](https://cloud.githubusercontent.com/assets/47926/5593034/391af01a-9201-11e4-99c6-ea20dbcceb43.png)