Add support for multi-valued date fields

Problem/Motivation

If a content type (say Event) has a multi-valued date field, then only one the first occurence of the event is shown on the calendar.

We should add support for multi-valued date fields.

Features requested:

1. For a multi-valued date field, display entry in calendar for each of the date values
2. For each entry on calendar, display the time of that instance. This is needed because field formatter will display all dates for all date instances