[WIP] Support Traffic Sign

Note

This is an ongoing Pull Request, not finished yet, please do not merge for now.

To display Traffic UI

To use drag-and-drop function powered by TouchScript

Add TouchManager to the Hierarchy.
[Optional] Add Cursors to the Hierarchy to display when tap, mainly for debugging, should not be included in the final beta build.
Add Standard Layer Component to Main Camer in the scene, in most cases, just enable Hit 3D Objects for interaction with 3D GameObject. Enabling all of them may result in failing to detect the actual object the cursor is hitting.
For the 3D GameObject you want to drag-and-drop, add Component Transformer, Transform Gesture, and a Collider. In our case, please only enable Translation in the Transform Type in Transform Gesture and remain other settings unchanged.
If you want to add an event handler for the mouse interaction, refer to DraggableTrafficSign.cs in our project, or view https://github.com/TouchScript/TouchScript/wiki/Examples or https://github.com/TouchScript/TouchScript/wiki/Gestures.

To use traffic sign mechanic

Copy Player1_TrafficSignLibrary and Player2_TrafficSignLibrary from PlayScnene_TrafficRule scene to your scene.
Refer above GameObjects in GameManger (If you don't want to use the traffic sign mechanic in your scene, just refer to an empty GameObject for now)
For the track block you want to make it traffic-sign-holdable, add TrafficSignHolder script as a component to it.
To resize the GameObject standing on the track block after dropping that traffic sign, please directly resize the StandingSign_xxx in the Prefabs folder, it will automatically take effect for all scenes.
To implement the actual traffic rule functions, @YuehCorazon please implement it in StandingTrafficSign.cs proper blocks (I've already added TODO keywords).

[x] Implement the UI display logic of Traffic Signs.
[x] Support dragging traffic signs in the editing phase (with turn-based control).
[x] Support dropping on the blocks with TrafficSignHolder component. (will calculate the closest one, see DraggableTrafficSign.cs for details)
[x] Support changing the style from flat traffic signs to standing traffic signs after dropping onto traffic sign holder block (should refer to the corresponding 3D Prefab in Unity Editor Inspector, see DraggableTrafficSign.cs for details).
[x] Remove the TileMechanics component from the current TerrainFlat prefab. We may discuss the implementation details later @YuehCorazon
[x] Setting proper Colliders for triggering the traffic rule.
[x] Implement the UI pagination logic of traffic signs @aartiDBarai.
[x] Implement the traffic sign selection limit logic.
[x] Setting traffic sign standing points for each block.