Tests for (editor) settings.
Bulletproofing of settings. Closes #81.

Inspired by jkuczm and littlepea/django-editor#3.
Updated Django version.
Document templates. Closes #87.
Slight fixup for unsubscribe e-mail text.
HTML-equivalents of standard templates.
Catch email related exceptions only.

Related to #12.
Catch typo.
Strip whitespace from rendered subjects.
Fix for #74.
Run subscribe tests with invisible newsletter.

Closes #69.
Catch general socket errors for mail submission.

An addition to 57620b658988aac6970bf0fa2467ef742b95bcb1 to get tests to run with no connection to the outside world.

Also see #92.