Instead of hard-coding 22 in random places, just make the following
widgets have a fixed height of 22 by default: Button, CheckBox,
ColorInput, ComboBox, RadioButton, SpinBox, TextBox.
In the future we can make this relative to the current font size,
but for now at least this centralizes the setting a bit better.
You can now enter a specific color as #rrggbb instead of clicking your
way through the color picker.
If you still want the color picker, just click the little color rect in
the widget and we'll bring up a ColorPicker. For a visual cue that this
rect is interactive, we use a hover hand cursor when hovering the rect.
ColorInput is a new GUI component for selecting color using ColorPicker dialog.
It is simplify usage of ColorPicker dialog and more elegant view of current selected color.
