[deps] remove html5lib, requests, webtest.

upgrade gunicorn, django-ses, rollbar.

update minimum python-dateutil, django_webtest.

reorder

requirements.txt

 Django==1.11.28
+django_webtest>=1.9.7
 
-celery==4.2.1
-django-picklefield==1.1.0
+gunicorn==20.0.4
 
 dj_database_url==0.5.0
 psycopg2==2.8.4
 
-html5lib==0.999
-python-dateutil>=1.5
-python3-openid==3.0.10
-gunicorn==19.9
-requests==2.21.0
+celery==4.2.1
+django-picklefield==1.1.0
+
+python-dateutil>=2.8
 unicodecsv==0.14.1
 bleach==3.1.1
-boto==2.49.0
-django-ses==0.8.10
 py3-validate-email==0.1.11
-oauth2client==4.1.3
-rollbar==0.12.1
 pycryptodome==3.8.2
 
-django_webtest>=1.9
-webtest==2.0.18
+python3-openid==3.0.10
+boto==2.49.0
+django-ses==0.8.14
+oauth2client==4.1.3
+rollbar==0.14.7