override remove method on instance to behave as expected

#97 I have to say this was a fun one with a annoyingly simple solution.
Now calling `remove` on an instance has the expected behavior and simply deletes that instance.
Calling `remove` on the class will still behave the same way.

I would also suggest removing the `query=None` from storedobject's `remove` method as it behaves different without a query based on which database you are using. i.e. the behavior referenced in #97 is only present in one of the test cases (mongo).


running this test:
```python
def test_remove_without_query(self):
        self.Foo.remove()
        self.assertEqual(
            self.Foo.find().count(),
            4
        )
```
will fail with: 
```
======================================================================
FAIL: test_remove_without_query (tests.queries.test_update_queries.UpdateQueryTestCaseEphemeral)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/adam/code/modular-odm/tests/queries/test_update_queries.py", line 75, in test_remove_without_query
    4
AssertionError: 5 != 4

======================================================================
FAIL: test_remove_without_query (tests.queries.test_update_queries.UpdateQueryTestCaseMongo)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/adam/code/modular-odm/tests/queries/test_update_queries.py", line 75, in test_remove_without_query
    4
AssertionError: 0 != 4

======================================================================
FAIL: test_remove_without_query (tests.queries.test_update_queries.UpdateQueryTestCasePickle)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/adam/code/modular-odm/tests/queries/test_update_queries.py", line 75, in test_remove_without_query
    4
AssertionError: 5 != 4

----------------------------------------------------------------------
Ran 580 tests in 2.535s

FAILED (SKIP=18, failures=3)
```