changes

1 color scheme
2 reposition Q1 and Q2 to correspond to the same side of the slider with color scheme, follow the physlet color scheme
3 Potential = Contour, rename
4 text Q1 and Q2
05 august
added the field lines arrow heads from http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=539.new#new
add more functions in terms of the slider options