Datepicker should convert String (or Number) to Date

[dipold]

The problem:

When loading an entity with angular's $http/$resource, angular creates the model by using native JSON function and all dates/datetimes are converted to String or Number.
The Datepicker wait for a ng-Model value must be a Date object - currently it get a error!

Workaround:
Convert the String (or Number) to Date in the Datapicker directive.
There are in angularjs a jsonStringToDate function in date $filter that makes this job

[pkozlowski-opensource]

@dipold We've started down the "automatically covert strings to Dates" route in the https://github.com/angular-ui/ui-date and it was a disaster. There are simply way too many formats that would could automatically handle. The proper solution is to use formatters / parsers (or a custom directive that would take care of conversions).

Going to close this one as we are just discussing plugging into the ngModel machinery in #612. Let's move the discussion there.