correlation_game

Initial correlation_game

Changes from version displayed at 9:30am 5/28/2014:

Changed answer input to slider. 
Changed scoring rules so that slider answers some distance away from true correlation are given partial credit.
Size of plot fixed to 400px by 400px.
Plot limits are fixed, prevents ellipse from rescaling plot.
Show options moved to left panel.  
Left panel size increased to 4/12, plot panel size increased to 8/12.  Right panel removed.
Lines of averages have bar(X), bar(Y) labels.
Flavor text for answer responses added.  Flavor text display is a function of distance of answer to true correlation.
True correlation displayed when an answer is given within a small range of the true correlation.
Difficulty now changes generating line slope and available "show" options, not answer tolerance.