WIP tags: REST API addition

Addition of rest api for tags.
Still work in progress.
Python is not Java, be lazy.
```python
class TagError(Exception):
    def __init__(self, error_msg=None, error_code=None):
        super(TagError, self).__init__()
        self.error_msg = error_msg or self.__class__.__name__
        self.error_code = error_code or 400
    def __repr__(self):
        return "{error_code}: {error_msg}".format(**self.__dict__)
    def __str__(self):
        return self.__repr__()

class TagOwnerError(TagError): pass

class TagNotFetchedError(TagError): pass

...

>>> raise TagNotFetchedError()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
__main__.TagNotFetchedError: 400: TagNotFetchedError
```