Add first version of server-side filtering of HTML with bleach

Fix formatting (pep8 and otherwise)

Make the CleanHtml a mixin so it can be used easier, add a test case

Mark HTML fields as 'safe' in the template

Update list of allowed HTML tags, take special care for reportlab

Add heading tags to white list

Rename get_clean_html to get_clean_html_fields
Added html support for motion text.
Use html parser 'beautifulsoup' to replace html tags which not supported by reportlab pdf.
'pip install bs4' required.

Fixed nested ol lists and unicode warning.

New requirement: beautifulsoup4