Smarter start date/end date selection

[atironati]

Right now start and end date selection in calendeer is a little weird. I know it's "by design" but as an experienced veteran of calendar widgets I expect more from my date selection:

If a range is currently being represented by calendeer, then selecting anything before the start date of the range should be a new start date, and selecting anything after the end date of the range should be a new end date.

Edit: