Enclosed body parts in s_body div to separate them from the head div.

Removed the 'stick' class, applying these styling rules instead to divs inside #s_body.

Removed the 'bodyPart' class, applying these styling rules instead to divs inside #bruce.

Fixed a bug where a left position other than 50% caused the elbow and knee joints to break. Fixed this by making the margin-left apply only to direct children of s_body instead of all children and by applying the left 50% property to #bruce only instead of all divs inside.

R=mikelawther@chromium.org

Review URL: https://codereview.appspot.com/48730044