Timezone controlpanel

Moved over timezone controlpanel from p.a.event. This needs also plone.app.vocabularies 2.1.15 (at time of writing unreleased). Timezones are not p.a.event specific (think about published dates, effective dates and so on) so in future we want to use them more.

This merge makes most sense together with plone.app.event 2.0 where the controlpanel was removed. Without p.a.e 2.0 we would have two controlpanels for date/time related settings. It wont hurt but confuse users. 

@thet please have a look at this.