chore - get tests passing for 3.7 python

Updates to travis.yml to support 3.7

Added aspell packages from flask-security/develop

Update pytest version (from flask-security-develop)

Upgrade pony to 0.7.4 to get 3.7 support.

Upgrade bcrypt to try to get it to compile under xenial travis dist

Change pypy specification in travis.yml for xenial dist.

Add minimal werkzeug version since latest 15.2 no longer works will low version Flask.

Removed all manual installing pypy

Bump minimum version of Flask to pick up pypy3 fixes.

setup.py

@@ -47,7 +47,7 @@
 ]
 
 install_requires = [
-    'Flask>=0.11',
+    'Flask>=0.12',
     'Flask-Login>=0.3.0',
     'Flask-Mail>=0.7.3',
     'Flask-Principal>=0.3.3',