Textbox widgets: make onChange fire when user is finished changing value

[bill]

For Textbox, ValidationTextbox, and related widgets (especially DateTextBox), onChange() should only be called when

• the value has changed

AND you have "finished entering the value", which means concretely:

• when widget blurs because
  • you tabbed away
  • you clicked another field or a blank area of the screen
• when you select a date from the calendar drop down

But, the validation checks (which make the box turn yellow when you have typed something invalid) should happen on every keystroke, so there needs to be some refactoring. (The listenOnKeyPress flag should be removed and assumed to be always true.)

[Douglas Hays]

(In [9601]) Fixes #3609. Added intermediateChanges boolean to control onChange frequency. Added priorityChange boolean to setValue to indicate if onChange should be called.

[Douglas Hays]

(In [9609]) References #3609. Make ComboBox? work by forcing onChange to fire.

[bill]

(In [10431]) Set incrementalChanges=true for sliders in GFX demos, to work like they used to. Refs #3609.