Changes for https://github.com/affiliatewp/AffiliateWP/issues/249

A few things I've noticed with https://github.com/affiliatewp/AffiliateWP/issues/249. I think we can be more efficient. The fixed widths for the columns are also causing issues as shown below.

Visits page with old CSS:
![screen shot 2014-07-14 at 8 48 39 pm](https://cloud.githubusercontent.com/assets/52581/3568688/421f9d22-0b34-11e4-96f9-fd829f7d08df.png)

Referrals page at mobile size with old CSS
![screen shot 2014-07-14 at 8 48 23 pm](https://cloud.githubusercontent.com/assets/52581/3568689/4222ef5e-0b34-11e4-813d-dba7a41eb1b8.png)

The Affiliates page with old CSS. It goes a little whack at certain sizes still due to max-width.
![screen shot 2014-07-14 at 8 46 52 pm](https://cloud.githubusercontent.com/assets/52581/3568692/4229c270-0b34-11e4-913b-42bdb855e984.png)

Affiliates page with old CSS. Note the empty space on the right.
![screen shot 2014-07-14 at 8 47 28 pm](https://cloud.githubusercontent.com/assets/52581/3568693/422a4f42-0b34-11e4-8efd-bf77f87f3fba.png)

The standard WP Posts section is nice and fluid so we should stick to percentages
![screen shot 2014-07-14 at 8 47 49 pm](https://cloud.githubusercontent.com/assets/52581/3568691/42281e02-0b34-11e4-8176-79a82c34d651.png)

Affiliates page - new CSS. More inline with how WP currently feels
![screen shot 2014-07-14 at 8 59 02 pm]
(https://cloud.githubusercontent.com/assets/52581/3568762/2de93a42-0b35-11e4-91de-0ad299bcbc24.png)

Affiliates page - new CSS - 1024
![screen shot 2014-07-14 at 9 01 12 pm](https://cloud.githubusercontent.com/assets/52581/3568775/7af5024e-0b35-11e4-9498-1cc12b345e76.png)

Affiliates page - new CSS - 800
![screen shot 2014-07-14 at 9 02 34 pm](https://cloud.githubusercontent.com/assets/52581/3568782/a4f539f6-0b35-11e4-9f69-a9255845430e.png)

Affiliates page - new CSS - 640
![screen shot 2014-07-14 at 9 04 43 pm](https://cloud.githubusercontent.com/assets/52581/3568799/f2c068ae-0b35-11e4-8b12-3323b434d88f.png)