-Events system update order is now choosen according to system priority

-added mixin for adding exluded components using it's type
-demos:
 *added GUI for selecting templates and choosing tools
 *change SpaceInvades SideMove system to not using events for better performance and multithreading
 *added Entites spawning support
 *fixed some Snake demo bugs
 *GUI work's better now

demos/source/gui/template_.d

@@ -0,0 +1,9 @@
+module gui.template_;
+
+import ecs.entity;
+
+struct TemplateGUI
+{
+    const (char)* name;
+    EntityTemplate* tmpl;
+}