Add a date picker for speech and section forms.

Bootstrap has been removed, but we were still trying to use the
bootstrap date and time pickers. Replace the date picker with
a foundation one. For the moment we'll just put the time picker
back to a text box with a placeholder.

I can't see autoclose mentioned in the fdatepicker docs, so I've
taken that out - the new datepicker seems to close when a date is
selected anyway.

Fixes #366.
Don't set a minimum end date based on start date.

With this as it was, if the start date were erroneously set too far
in the future, and then brought back, the picker for the end date
was stuck with only accepting dates after the original start date.

We should have a proper think about how to make the javascript keep
the dates and times consistent.
Localize formats of dates when adding speeches and sections.

The formats for acceptable dates and the placeholders now change
depending on the language you ask for.