Gamepad support

[FlipWebApps]

Not all of the components work as expected with gamepad or keyboard input. Add such support using the included GameStructure demo as a basis.

Some suggestions of what needs doing:

Part 1 - Title Screen

• Navigation of buttons.
• Settings window
• Press a certain button to continue

Part 2 - Level Selection Screen

• Navigation of buttons.
• Select follows highlighted UI element ensuring correct actions (e.g. can't proceed with a locked button)

Part 3 - Character Selection Screen

• Navigation of buttons.
• Select follows highlighted ensuring correct actions (e.g. can't proceed with a locked button)

Part 4 - Game

• Navigation of buttons (or do we need this - should perhaps just trigger pause window on a specific key press)
• Support within gameover and pause windows.

Thoughts on some of the key changes that might need doing:

• Setup an initially selected UI element in the scenes Event System and enable navigation for buttons and other prefabs.
• DialogInstance should have a 'First Selected' field and record / return the last selected item when shown / closed.
• Change MouseClickOrTapXxx components - ButtonOrTapXxx and add options for specifying button(s?) to react to.