Fix bugs in all examples

[hanson-hschang]

Make sure each example file is clear and runnable without any issue. That means:

• check comments if they are clear

• check the generated .blend file if the rendering is the same as expect

• [x] camera_movement.py

• [x] pose_demo.py

• [ ] projectile_motion.py

• [ ] pendulum.py

• [ ] elastica_timoshenko.py

• [ ] update single_rigid_rod_spring_action.py

• [ ] br2\br2_pushed.py with br2\callbacks.py

[shaoweibai]

"projectile_motion.py" & "pendulum.py":

1. All the "set_keyframe" need to be change to "update_keyframe"
2. File "Sphere" cannot be located from the route "bsr.geometry"

"elastica_timoshenko.py", "single_rigid_rod_spring_action.py", "callbacks.py": Fine

"br2_pushed.py":

1. line 226: 'FrameManager' object has no attribute 'set_frame_end'