Changed CSS so that mark is not steel blue as mark is the definition for
blocked cells
finished drag and drop which allows user to only move into selected
shades
debugged previous error of shades not going back to normal after
unselected

Change-Id: Ie9687a3fd052f192b94fbd84f46d4abc7128d284
Signed-off-by: taoman89 <juntao.zhu.2010@sis.smu.edu.sg>