Ui date fix date parrse and refactor

[ivan-zakharchuk]

Fixes #120

Here we have following breaking changes - now all input date strings will be converted to instance of Date if possible and $viewValue will be formatted by $.datepicker default params or they might be provided explicitly via ui-date="opts" and if we want to change format in model we could use ui-date-format as datepicker format string.

[alexanderchan]

Thanks for this, sorry for the delay as I was away. The breaking changes worry me as we have had issues created for those in the past and the validator is now removed which I think is nice to use with angular form errors.

I think I'm ok to implement if you're willing to help with issues created moving forward against this in case people are still using these features, but otherwise I could see more work coming from breaking changes.

Would you be up for watching and helping? Thanks!

[ivan-zakharchuk]

Thank you for review. I'll take a look into details and give you answer at this weekend.