Expose more events and/or bindable properties from date picker + date range picker

[hmnd]

It is not currently possible to externally know the state of which months are currently visible to the user or to programmatically navigate the user to a different month.

Such functionality would be immensely helpful for building on top of the date pickers, allowing developers to add buttons to skip to a particular month, or displaying availability within the calendar as the user navigates.

[huntabyte]

To determine what months are visible, you can use a combination of the placeholder (by binding to it or listening for changes via onPlaceholderChange) and visibleMonths to determine that.