Thrown Item Physics (#120)

* Thrown object speed is now based on force.
Fixed BoundingBox namespace.

* 100% more throwing.
CollisionGroup enum.

* Update Engine.

Content.Shared/Physics/CollisionGroup.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace Content.Shared.Physics
+{
+    /// <summary>
+    ///     Defined collision groups for the physics system.
+    /// </summary>
+    [Flags]
+    public enum CollisionGroup
+    {
+        None = 0x0000,
+        Grid = 0x0001, // Walls
+        Mob = 0x0002, // Mobs, like the player or NPCs
+        Fixture = 0x0004, // wall fixtures, like APC or posters
+        Items = 0x008, // Items on the ground
+    }
+}