oauth_verifier required, remove simplejson dependency, update endpoint

* Update `updateProfileBannerImage` to use the v1.1 endpoint

* Added `getProfileBannerSizes` method using the GET
/users/profile_banner.json endpoint

* Fixed a couple of endpoints using variable in the url:
  * destroyDirectMessage, createBlock, destroyBlock no longer use id in
their urls, this shouldn't break anything though.
(t.destroyDirectMessage(id=123) should still work)

* `oauth_verifier` is now **required** when calling
`get_authorized_tokens`

* Updated docs - removed getProfileImageUrl docs since it is
deprecated. Noted since `Twython` 2.7.0 that users should focus on
migrating to v1.1 endpoints since Twitter is deprecating v1 endpoints
in May!,