[Framework-Team] date widgets for Plone 5

[David Glick (Plone)]

Currently we have way too many date and datetime widgets in core:
- Archetypes
- z3c.form
- collective.z3cform.datetimewidget (added as an override of the default 
z3c.form one by plone.app.z3cform; uses jquerytools date picker)
- plone.formwidget.datetime (added by plone.app.event; uses jquerytools)
- plone.app.widgets (uses pickadate)

The latter 2 offer both Archetypes and Dexterity compatible widgets, and 
we should standardize on one of them for Plone 5. Rok and Johannes, can 
you make a recommendation?