Fix decorators

Close #52 - decorator absorbing arguments.

This fix makes some small changes to how the decorator works:

* Removal of the optional ```methods``` parameter as only HTTP POST and GET requests are allowed by the Twilio service, so there is redundancy in the option to use other methods.

* Removed the optional ```blacklist``` parameter as this was ambiguous: the parameter should have been named ```check_for_potential_blacklisted_caller``` or similar. On further investigation, a setting in Django-Twilio called [```DJANGO_TWILIO_BLACKLIST_CHECK```][1] determined the exact same thing. By default, the caller is always checked. As this is good practice and there was already a manual way of deciding on blacklist checking, I believe we do not need it at this point.

Further to this, the decorator was absorbing the arguments *anyway*, so this change should not affect any current users, as they wouldn't be able to actually use the functionality beforehand!



[1]: http://django-twilio.readthedocs.org/en/latest/settings.html#django-twilio-blacklist-check-optional


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