Make setup.py executable
bootstrap3: add test for html.add_css_class
bootstrap3: teach add_css_class to prepend classes

Also update tests
bootstrap3: prepend generic class to input forms to user supplied ones

This let the user passing custom classes to widgets override the
bootstrap defaults.
Merge pull request #147 from xrmx/prependclasses

Make it easier to override default bootstrap style for input forms
Release 4.8.1
Merge branch 'release/4.8.1'