Implement thread-safe ChatBot API (#1510, #1579)

+ Rework task scheduling in chatbots
+ Switch back terrain processing to tasks

MinecraftClient/TaskWithDelay.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace MinecraftClient
+{
+    /// <summary>
+    /// Holds a task with delay
+    /// </summary>
+    class TaskWithDelay
+    {
+        private Action _task;
+        private int tickCounter;
+        private DateTime dateToLaunch;
+
+        public Action Task { get { return _task; } }
+
+        public TaskWithDelay(Action task, int delayTicks)
+        {
+            _task = task;
+            tickCounter = delayTicks;
+            dateToLaunch = DateTime.MaxValue;
+        }
+
+        public TaskWithDelay(Action task, TimeSpan delay)
+        {
+            _task = task;
+            tickCounter = int.MaxValue;
+            dateToLaunch = DateTime.Now + delay;
+        }
+
+        /// <summary>
+        /// Tick the counter
+        /// </summary>
+        /// <returns>Return true if the task should run now</returns>
+        public bool Tick()
+        {
+            tickCounter--;
+            if (tickCounter <= 0 || dateToLaunch < DateTime.Now)
+                return true;
+            return false;
+        }
+    }
+}