Add a defautl style attribute in FormView

[kinderp]

When a lot of items in self.styles share the same style commands (e.g. locations, start_and_end_date_parts, available_languages) it could be useful a __default item
to apply the same style in only one command.

        self.styles = {
            'event_name_and_session_id': {
                'style': 'Normal',
                'space': 4.5,
                'commands': [
                                ('alignment', TA_CENTER),
                                ('fontName', 'Helvetica'),
                                ('fontSize', 18),
                            ]
            },
            'vendor': {
                'style': 'Normal',
                'commands': [
                                ('alignment', TA_CENTER),
                                ('fontSize', 12),
                            ],
                'space': 4.5,
            },
            'start_and_end_date_parts': {
                'style': 'Normal',
                'commands': [
                                ('alignment', TA_LEFT),
                                ('fontSize', 8),
                            ]
            },
            'locations': {
                'style': 'Normal',
                'commands': [
                                ('alignment', TA_LEFT),
                                ('fontSize', 8),
                            ]
            },
            'available_languages':{
                'style': 'Normal',
                'commands': [
                                ('alignment', TA_LEFT),
                                ('fontSize', 8),
                            ]
            }
        }

Take a look at render() function in form_view.FormView