Allow access from remote hosts

A recent change to Notebook (5.6.0) prevents access from remote hosts by default.
This change unconditionally re-enables that ability since remote access is a primary
tenet of Kernel Gateway.

Also dropped python 3.3 from the travis matrix since setuptools no longer supports
it (as of May 24) and was generating a failure during the installation phase.

Fixes #293

.travis.yml

@@ -2,7 +2,6 @@ sudo: false
 language: python
 python:
     - 2.7
-    - 3.3
     - 3.4
     - 3.5
     - 3.6

kernel_gateway/gatewayapp.py

@@ -457,7 +457,9 @@ def init_webapp(self):
             kg_personality=self.personality,
             # Also set the allow_origin setting used by notebook so that the
             # check_origin method used everywhere respects the value
-            allow_origin=self.allow_origin
+            allow_origin=self.allow_origin,
+            # Always allow remote access (has been limited to localhost >= notebook 5.6)
+            allow_remote_access=True
         )
 
         # promote the current personality's "config" tagged traitlet values to webapp settings