Resolve a few plugin loading and scheduler issues

Author: ethanhann

src/InEngine.Core/PluginAssembly.cs

@@ -98,12 +98,12 @@ static Assembly LoadPluginEventHandler(object sender, ResolveEventArgs args)
         static string MakeFullPluginAssemblyPath(string pluginName)
         {
             var plugins = InEngineSettings.Make().Plugins;
-            if (!plugins.ContainsKey(pluginName))
+            var isCorePlugin = Assembly.GetCallingAssembly().GetName().Name == pluginName;
+            if (!isCorePlugin && !plugins.ContainsKey(pluginName))
                 throw new PluginNotRegisteredException(pluginName);
-            
             return Path.Combine(
                 Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location),
-                plugins[pluginName],
+                isCorePlugin ? "" : plugins[pluginName],
                 $"{pluginName}.dll"
             );
         }

src/InEngine.Core/Scheduling/SuperScheduler.cs

@@ -7,7 +7,7 @@ namespace InEngine.Core.Scheduling
 {
     public class SuperScheduler
     {
-        public Schedule Schedule { get; set; }
+        public Schedule Schedule { get; set; } = new Schedule();
         public IScheduler Scheduler { get; set; }
         public string SchedulerInstanceName { get; set; } = "InEngine";
         public string SchedulerThreadPoolType { get; set; } = "Quartz.Simpl.SimpleThreadPool, Quartz";
@@ -23,7 +23,6 @@ public void Initialize()
                 ["quartz.threadPool.threadPriority"] = SchedulerThreadPriority
             }).GetScheduler();
 
-            Schedule = new Schedule();
             PluginAssembly.Load<IPlugin>().ForEach(x => {
                 x.Plugins.ForEach(y => y.Schedule(Schedule));
             });

src/SampleMvcWebsite/Global.asax.cs

@@ -22,7 +22,7 @@ protected void Application_Start()
 
         protected void Application_End()
         {
-            SuperScheduler.Shutdown();
+            SuperScheduler?.Shutdown();
         }
     }
 }