Introduce input modes and Pause Menu (#8)

- Add input mode switching to the Input Manager
- Automatically set input mode on scene load - UI for MainMenu and GameAndUI for other scenes
- Add PauseMenu prefab, auto-loaded via the boostrap system
- Automatically control PauseMenu visibility based on current scene

Co-authored-by: AlexanderT <alexander@foolhardyhorizons.com>
Co-authored-by: Michal Pikulski <michal.a.pikulski@gmail.com>
Reviewed-on: #8

Assets/Scenes/Levels/AppleHillsOverworld.unity

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