Provide another way to send data to gitlab with a new `query_parameters`
argument. This parameter can be used to explicitly define the dict of
items to send to the server, so that **kwargs are only used to specify
python-gitlab specific parameters.

Closes #566
Closes #629

The integration tests failed because a test called 'decode()' on a
string-type variable - the GitLabException class handles byte-to-string
conversion already in its __init__. This commit removes the call to
'decode()' in the test.

```
Traceback (most recent call last):
  File "./tools/python_test_v4.py", line 801, in <module>
    assert 'Retry later' in error_message.decode()
AttributeError: 'str' object has no attribute 'decode'
```

Add support to resource label events

Closes #589

Closes #611

This images is updated to the latest GitLab CE.

Fix the diff() test to match the change in the API output.

Fix the bytes/str issues

Also consolidate project/group badges tests, and add some docs

Fixes #469