Fix jdk8_20 compilation.
Support for DatePicker validation.
Possibility to skin validation tooltip by css.
Helper metods to get validaton Decorators and show tooltips on demand.
 - whole project is compatible now with javafx 8.40 beta
 - validation support for datepicker
 - better ability to css customization
 - more freedom of decoration creation (support for lambda expression)
 - ability to create decoration using FontAwesome font.
 - support for observable status of validation group
 - some helper methods
Merge pull request #21 from nonameplum/master

Merge from branch nonameplum