Timepicker and datepicker functionnality

This pull request includes two patches, one for Datepicker, the other for Timepicker.

In datepicker, a new date type was added : "iso". It allows to have a uniform, ISO format, representation in the scope that can be shared between elements in the application, the database, etc.

In timepicker, it fixes a problem with default value, where the widget would conflict with angular scope values. The directive now takes care of resolving conflicts. It also adds support for the widget options and a behavior tweak.

Tests are added for the new features.