Added stripping of whitespace for SlugField and URLField
Merge pull request #1113 from denibertovic/master

Fixed #18761 -- Added whitespace stripping to URLField and SlugField.
Fixed #19436 -- Don't log warnings in ensure_csrf_cookie.
Moved IgnorePendingDeprecationWarningsMixin in django.test.utils.

This mixin is useful whenever deprecating a large part of Django.
Fixed #20444 -- Cookie-based sessions does not include a remote code execution-warning
Add missing imports and models to the examples in the the model layer documentation
Add missing imports and models to the examples in the view layer documentation
Add missing imports to the examples in the 'First Steps'