Starting process of moving lots of similar date handling and navigation code out of Date and Calendar and into the Date API where we can use the same code everywhere. Adding a flexible date argument to the API that will work on any Views date field and take any ISO date argument. Adding an argument default option to set a missing date argument to the current date that will work on any date field. Adding a date back/next navigation attachment that works with the date argument and which can be attached to any view. Next step will be to go in and adapt the Calendar module to share this code instead of creating its own.