Fix min date

[t0m3k]

Multiple fixes:

• minDate and maxDate setting now includes the dates provided. Before, if minDate was provided using new Date(), comparison would be made using nanoseconds. Since new Date() value was created on page load, it would be in the past, making today's date not selectable. Similar could happen on end date in some cases. Now as long as day is matching both dates will be included. Issue Selecting current day gets the previous day #117
• ColorKey and Colors types were created for type safety. Now, users using datepicker will see types for colorPrimary based on COLORS constant. COLORS constant will also enforce all color types to be including new colors using Colors interface.

[onesine]

Thanks for this PR @t0m3k