set correct logo ratio

Related to #7.
I will try to make Gold sponsors feel they are distinguished from
the Silver sponsors. But if we put 3 gold sponsors in a row:

    | Gold 1 | Gold 2 | Gold 3|
    | ...... | ...... | ..... |

I fell it is too densed to read.
improve sponsor content, work on #5

- deadline --> due
- make sponsor information clearer, follow pycon.us
combine sponsor application and info, work on #6