datepicker dynamic min-mode and max-mode

[Slimmmo]

Simply enabling the ability to change modes dynamically without having to use two different datepickers and hiding one based on the current mode.

Also fixes min-mode for popups. #2618

[wesleycho]

Can you add a test for this? I will merge this afterwards - otherwise this looks good.

[Slimmmo]

Hi Wesley,

I made a little change since you posted to make it slightly more fool-proof. If you update min-mode to something larger than datepicker-mode, it will now automatically update datepicker-mode to match min-mode. Likewise for max-mode but for smaller values.

Please let me know if those tests aren't adequate. There isn't really that much to test though.

Thanks.

[wesleycho]

I need to review this deeper - the split off of the minMode and maxMode from the original iterator into a custom one has me wary.

[wesleycho]

Thanks for this work - in the future though, please squash the commits. It ended up being quite a pain resolving the conflict multiple times because the commits were never squashed.