new jquery based widgets for Time/Date/DateTime, backported from crm

introduce a default render implementation on the base widget, which add_media and then call the newly introduced method _render(form, field, formrenderer), abstract of the base widget class. This allow a litle code factorisation and avoid to forget the call to add_media in subclasses.

[forms] new optional suffix attribute on widget objects, used to generage input name / dom id. Ease reuse of widgets from another widget. Also move base values computing to a separated values(form, field) method.