Must-have features before release

[OverloadedOrama]

• Shortcut deleting to allow for actions without binding.
• Allow adding multiple shortcuts for a single action, like in Godot's Input Map. Useful for having alternatives and handling multiple input devices, such as having a keyboard and a gamepad shortcut for the same input action.
• Grouped input actions and group-within-group input actions.
• Shortcut editing.
• Toggle which event types can be changed.
• If there are shortcut conflicts in two actions, give the user the option to re-assign the binding.
• Global group input actions and local group input actions. Global shortcuts can only be mapped to one action in the entire project, while local shortcuts can be mapped to multiple actions in the project, but not to actions in the same group.
• Choose between different presets. Default presets cannot be modified.