Adjusted EDV volatility by 50%

This change was taken from James Crocker's code.
Here is his explanation of the idea:
 Added a .5 factor for the EDV ETF as per Mr. Grossman's
 blog entry (EDV has 50% higher volatility than the other basket items).

Signed-off-by: Ed Bartosh <bartosh@gmail.com>
Simplified data structure of context.stocks

Used list instead of dictionary as the keys were not used
anywhere in the code.

Signed-off-by: Ed Bartosh <bartosh@gmail.com>