Main menu and tool code refactoring (#656)

* Refactoring LinearToolButton into a more generic skinnable button
* Renamed BaseUI and menu button classes and moved some generic files into U/
* Get properties in UButton are now abstract functions
* Replaced graphics loading for UIMainButton with new Atlas code
* Skinnable BaseUButton and generalized with MainMenuButton
* ButtonSkin allows overriding background
* Main menu is scaled to screen size fraction
* LoadingExtension.ModUi is now a singleton ModUI accessible via ModUI.Instance
* Fixed main button to always 50px. Added min scale for main panel button 40px
* UI scale slider affects mainmenu panel now
* Toned down button textures; added v11 to 11 in main button; Review notes satisfied
* MenuLayout class responsible for menu row breaking and sizing

Author: kvakvs

TLM/CSUtil.CameraControl

@@ -20,7 +20,7 @@ public void CustomClickNodeButton(ushort nodeId, ref NetNode data, int index) {
                     data.m_flags |= NetNode.Flags.CustomTrafficLights;*/
 
                 // NON-STOCK CODE START
-                ToggleTrafficLightsTool toggleTool = (ToggleTrafficLightsTool)UIBase
+                ToggleTrafficLightsTool toggleTool = (ToggleTrafficLightsTool)ModUI
                                                           .GetTrafficManagerTool(true)
                                                           .GetSubTool(ToolMode.SwitchTrafficLight);
                 toggleTool.ToggleTrafficLight(nodeId, ref data, false);

TLM/OptionsFramework

@@ -73,8 +73,6 @@ public class ManualHarmonyPatch {
         /// </summary>
         public static Translation TranslationDatabase = new Translation();
 
-        public static UIBase BaseUI { get; private set; }
-
         public static UITransportDemand TransportDemandUI { get; private set; }
 
         public static List<ICustomManager> RegisteredManagers { get; private set; }
@@ -368,10 +366,10 @@ void Destroy<T>() where T : MonoBehaviour {
                 }
 
                 Log.Info("Removing Controls from UI.");
-                if (BaseUI != null) {
-                    BaseUI.Close(); // Hide the UI ASAP
-                    Object.Destroy(BaseUI);
-                    BaseUI = null;
+                if (ModUI.Instance != null) {
+                    ModUI.Instance.Close(); // Hide the UI ASAP
+                    Object.Destroy(ModUI.Instance);
+                    ModUI.SetSingletonInstance(null);
                     Log._Debug("removed UIBase instance.");
                 }
 
@@ -544,9 +542,10 @@ public override void OnLevelLoaded(LoadMode mode) {
             }
 
             Log.Info("Adding Controls to UI.");
-            if (BaseUI == null) {
+            if (ModUI.Instance == null) {
                 Log._Debug("Adding UIBase instance.");
-                BaseUI = ToolsModifierControl.toolController.gameObject.AddComponent<UIBase>();
+                ModUI.SetSingletonInstance(
+                    ToolsModifierControl.toolController.gameObject.AddComponent<ModUI>());
             }
 
             // Init transport demand UI