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/Prefabs/Managers/InputManager.prefab

@@ -72,6 +72,6 @@ MonoBehaviour:
   m_ActionEvents: []
   m_NeverAutoSwitchControlSchemes: 0
   m_DefaultControlScheme: 
-  m_DefaultActionMap: DefaultActionMap
+  m_DefaultActionMap: 53d55b3c-f7c2-4706-a857-c615ecb16ff7
   m_SplitScreenIndex: -1
   m_Camera: {fileID: 0}