Made requirements.txt py36-compatible

Some packages had to be removed; they are deployment-specific anyway,
and may not even be needed any more.

I've also added some secondary requirements that weren't specified yet.
The next steps will be to split into runtime and development requirements.

requirements.txt

@@ -41,12 +41,13 @@ pytest-cov==2.3.1
 mock==2.0.0
 
 # Secondary requirements
-flup==1.0.2
 Flask-PyMongo==0.4.1
 Jinja2==2.8
 Werkzeug==0.11.10
+appdirs==1.4.2
 argparse==1.2.1
 cffi==1.6.0
+CommonMark==0.7.2
 cookies==2.2.1
 cryptography==1.3.1
 enum34==1.1.3
@@ -57,6 +58,8 @@ googleapis-common-protos==1.1.0
 ipaddress==1.0.16
 itsdangerous==0.24
 oauth2client==2.0.2
+oauthlib==2.0.1
+packaging==16.8
 pbr==1.9.1
 protobuf==3.0.0b2.post2
 protorpc==0.11.1
@@ -64,7 +67,8 @@ py==1.4.31
 pyasn1==0.1.9
 pyasn1-modules==0.0.8
 pymongo==3.2.2
+pyparsing==2.1.10
 requests_oauthlib==0.7.0
 six==1.10.0
-wsgiref==0.1.2
 coverage==4.0.3
+WTForms==2.1