Add practice set games exercise (http://en.wikipedia.org/wiki/Set_(game)...

The purpose of this program is to enrich current existing Khan Academy exercises
and for exploration of the environment in Khan Academy exercise platform.

This is not a full SET card games, but can be if there exist such demands :)

to know more about SET, checkout its wiki page http://en.wikipedia.org/wiki/Set_(game)
Signed-off-by: samsu <samsu.sempena@gmail.com>

![set games](https://f.cloud.github.com/assets/1615221/1816914/b2212426-6f5b-11e3-975a-ed22c854048e.png)