Gameplay: Player movement

[Helco]

The player should be able to move, we have to experiment with the scheme, possibly:

• "Stop-and-go" press select to start walking, press again to stop walking - left, right might stop walking
• "Hold-to-go" holding select to keep walking

We additionally need:

• Wall collision
• Steps (with max step height)
• Maybe sprite collision? (very optional rn)

[Helco]

Not much UX experimentation done, no time for that.

Fixed by 5e72193