feat(datepicker): Add initial view setting

[trevordaniels]

Partially addresses #165 Not sure if you want to expose CalendarViewType, or create a new export type similar to DatepickerMode

[harogaston]

Did you check what happens if initialView is not in the keys of config.mappings.changed? What I mean is the initialVIew must be part of the views asociated with the datepicker mode. For instance initialView=minute is not compatible with datepicker mode=year.

Does it behave well under those conditions? Otherwise a check must be added.

[trevordaniels]

Added a check to ensure the view exists in mappings.changed

[harogaston]

Nice, I mentioned it because I had already been thinking about implementing this. Keep it up!

[trevordaniels]

I appreciate your feedback, hope you hadn't started on it!