Editor GUI keyboard navigation

[0HyperCube]

• Add CSS focus style (Keyboard menu/widget navigation #628)
• Focus the primary button with .focus() when a popup is created (Keyboard menu/widget navigation #628)
• When a dialog is open, lock the user's focus within the dialog (currently they can ShiftTab to entries outside of the menu).
• Allow opening dropdowns (dropdown input and font input) with space
• Allow navigating dropdowns with arrow keys (however the rows should not be focused - as in the default browser implementation)
• Allow enter to select a dropdown entry.