rework scheduled tasks in preparation of common project going portable

MediaBrowser.Model/Tasks/TaskExecutionOptions.cs

@@ -0,0 +1,11 @@
+
+namespace MediaBrowser.Model.Tasks
+{
+    /// <summary>
+    /// A class that encomposases all common task run properties.
+    /// </summary>
+    public class TaskExecutionOptions
+    {
+        public int? MaxRuntimeMs { get; set; }
+    }
+}