Passing request to send_activation_email

This fixes #8 

Added an optional parameter `request` to `create_inactive_user`. If it is passed `send_activation_email` takes advantage of it by initializing `ContextRequest` which allows to reference all the extra variables added by template context processors.

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The reason I actually needed this is to generate absolute URLs in the generated email. This allows me to do this:

    http{% if request.is_secure %}s{% endif %}://{{ request.get_host }}{% url 'registration_activate' activation_key=activation_key %}

and once I will transition to Django 1.7 something like this is possible:

    {{ request.scheme }}://{{ request.get_host }}{% url 'registration_activate' activation_key=activation_key %}