Use a common requirements file

We can use newer setuptools and pbr to use environment markers in our
requirements files which allows us to select deps if the environment
matches. With this we restrict the email dep to python < 3.0 which is
the only dep we have that doesn't work across python 2 and 3.

Note that this also updates the pbr machinery to pull in this new
feature support. Part of this update requires updating hacking to avoid
conflicting pbr requirements. This in turn has created some churn in the
format of the code but should largely be a noop.

Change-Id: I0be5dd8a6b33a51329077b5a5f4c7f5576829956

storyboard/common/event_resolvers.py

@@ -70,7 +70,7 @@ def task_details_changed(event):
 
 
 def task_deleted(event):
-    #NOTE: There is nothing to resolve, as the task title is already stored in
+    # NOTE: There is nothing to resolve, as the task title is already stored in
     # the info. There is no way to store an id because the task is hard deleted
     # at the moment we would query it.
     return event