Rejig render method of SpeechTextFieldWidget to cope with Django 1.4.

Django 1.4 doesn't have the format_html method in django.utils.html
so work around this by using more of the render method from the
superclass (which is probably a nicer way to do things anyway).
Make sure there are two newlines between each </p> <p> pair.

If a user enters some paragraphs of their own (which for now just
means their first non-whitespace characters are <p>, then we need
to make sure there are two newlines between close and open paragraphs
so that the <p> and </p> can be removed at editing time and come
back on a save.
Avoid django.utils.html.remove_tags in Django 1.4

remove_tags doesn't exist in Django 1.4, so work around it.
Use StripWhitespaceField for Speeches.