add format type

[HawkeyePierce89]

Add sb-date-format attribute.

Usage:

<div sb-date-select ng-model="obj.date1" sb-date-format="DD-MM-YYY"></div>

or

<div sb-date-select ng-model="obj.date1" sb-date-format="toDate"></div>

or we can don't use this attribute, in this case will be used format "YYYY-MM-DD"

<div sb-date-select ng-model="obj.date1"></div>

And need approved this PR for add usage info this attribute