Add Oauth2 Bearer Token support

Basic implementation of authenticating with token instead of basic auth, as the auth=(login,password) flag on requests sends junk authentication as it overrides the bearer authentication header with a base64 encoded blank string.

webdav3/client.py

@@ -177,7 +177,7 @@ class Client(object):
             headers.extend(headers_ext)
 
         if self.webdav.token:
-            webdav_token = "Authorization: OAuth {token}".format(token=self.webdav.token)
+            webdav_token = "Authorization: Bearer {token}".format(token=self.webdav.token)
             headers.append(webdav_token)
         return dict([map(lambda s: s.strip(), i.split(':', 1)) for i in headers])
 
@@ -211,6 +211,17 @@ class Client(object):
         """
         if self.session.auth:
             self.session.request(method="GET", url=self.webdav.hostname, verify=self.verify)  # (Re)Authenticates against the proxy
+        if all([self.webdav.login, self.webdav.password]) is False:
+            response = self.session.request(
+                method=self.requests[action],
+                url=self.get_url(path),
+                headers=self.get_headers(action, headers_ext),
+                timeout=self.timeout,
+                data=data,
+                stream=True,
+                verify=self.verify
+            )
+        else:
             response = self.session.request(
                 method=self.requests[action],
                 url=self.get_url(path),