Add content to index page.  Switch button style through app
Switch to Slate theme from Bootswatch
Code cleanup

Changed button style from default to primary.  Removed encoding from a couple of variables.  Fixed mistake in portfolio table where td elements had been written as th elements.  Changed brokr bucks to BrokrBucks.
Updates to procedure to buy shares

Block purchase of shares if user does not have enough BrokrBucks.  Check to see if user already owns shares of the stock that they are trying to buy.  Inform user that they already own the stock and block the purchase (for now, this will be changed later). Require that user is logged in to view portfolio, buy_stock, and lookup_stock pages.