Added issuer to the transaction history grid

I think adding the column (Issuer) next to Amount will help users to understand one of the key concepts of Stellar: trust who is keeping the credit you own.

![screen shot 2014-08-05 at 11 26 32 am](https://cloud.githubusercontent.com/assets/428680/3816382/15e4e36a-1cce-11e4-8fdb-111f3b607d3d.png)

After talking to @thejollyrogers and @jedmccaleb, they don't want any issuer to show up for STR. They are probably going to have me change the account viewer to not show the issuer for STR. They say there is technically no issuer for STR, so we shouldn't show anything.