Fix Collection creation in test browser.

Do not visit /folder_factories to select 'Collection',
because that label is ambiguous: it can be old style Topic or new style Collection.
Just use the direct url with createObject.
Perhaps a bit uglier, but it works.
Back to development.
Use PLONE_APP_CONTENTTYPES_FIXTURE as test layer for Plone 5 compatibility.
Replace deprecated test assert statements.
Use .rst instead of .txt for CHANGES and README.
plone.portlet.collection should also install plone.app.querystring:default
profile
update CHANGES.rst
Merge branch 'master' into z3cform