Stunner - date/time UI validation

We have some Date/Time validation for Timer Events, and partially implemented Date/Time validation for User Task Notifications. Both implementations should be merged to one complete solution.

Also Time validation should be done for SLA property for all affected nodes.

References:

• Engine Date/Time documentation
• ISO engine implementation and unit tests
• Engine old time style
• UI Event Timers implementation
• UI Notification implementaion