Add URDF and XACRO files for iiwa7 robot and tool patron

- Created iiwa7_gazebo.urdf to define the iiwa7 robot model with detailed links, joints, and Gazebo integration.
- Introduced patron.xacro for the tool patron, including its inertial properties, visual representation, and collision geometry.

src/iiwa_description/worlds/iiwa.wbt

@@ -10,7 +10,7 @@ EXTERNPROTO "../resource/protos/Object.proto"
 
 WorldInfo {
   title "iiwa robotics"
-  basicTimeStep 10
+  basicTimeStep 32
   optimalThreadCount 4
   contactProperties [
     ContactProperties {
@@ -30,6 +30,13 @@ WorldInfo {
       softCFM 0.002
       maxContactJoints 100
     }
+    ContactProperties {
+      material1 "default"
+      material2 "default"
+      maxContactJoints 20
+      bounce 0
+      softCFM 0.001
+    }
   ]
 }
 Viewpoint {