Minor improvements to resetting code

- Reset state while the server is starting rather than once it has
   started. Hopefully fixes a weird issue where wireless modems wouldn't
   be "connected" on server startup.

 - Correctly reset the MainThread metrics on server start/stop.

src/main/java/dan200/computercraft/core/computer/MainThread.java

@@ -23,8 +23,8 @@ import java.util.concurrent.atomic.AtomicLong;
  * {@link MainThread} starts cool, and runs as many tasks as it can in the current {@link #budget}ns. Any external tasks
  * (those run by tile entities, etc...) will also consume the budget
  *
- * Next tick, we put {@link ComputerCraft#maxMainGlobalTime} into our budget (and clamp it to that value to). If we're
- * still over budget, then we should not execute <em>any</em> work (either as part of {@link MainThread} or externally).
+ * Next tick, we add {@link ComputerCraft#maxMainGlobalTime} to our budget (clamp it to that value too). If we're still
+ * over budget, then we should not execute <em>any</em> work (either as part of {@link MainThread} or externally).
  */
 public final class MainThread
 {

src/main/java/dan200/computercraft/shared/CommonHooks.java

@@ -29,7 +29,6 @@ import net.minecraftforge.event.*;
 import net.minecraftforge.event.entity.player.PlayerContainerEvent;
 import net.minecraftforge.eventbus.api.SubscribeEvent;
 import net.minecraftforge.fml.common.Mod;
-import net.minecraftforge.fml.event.server.FMLServerStartedEvent;
 import net.minecraftforge.fml.event.server.FMLServerStartingEvent;
 import net.minecraftforge.fml.event.server.FMLServerStoppedEvent;
 
@@ -90,22 +89,21 @@ public final class CommonHooks
         {
             ComputerMBean.register();
         }
-    }
 
-    @SubscribeEvent
-    public static void onServerStarted( FMLServerStartedEvent event )
-    {
-        ComputerCraft.serverComputerRegistry.reset();
-        WirelessNetwork.resetNetworks();
-        Tracking.reset();
+        resetState();
         ComputerMBean.registerTracker();
-        NetworkUtils.reset();
     }
 
     @SubscribeEvent
     public static void onServerStopped( FMLServerStoppedEvent event )
+    {
+        resetState();
+    }
+
+    private static void resetState()
     {
         ComputerCraft.serverComputerRegistry.reset();
+        MainThread.reset();
         WirelessNetwork.resetNetworks();
         Tracking.reset();
         NetworkUtils.reset();