Fix right-side overflow in landing page
Fix right-side overflow in landing page

Previous fix reverted in fb91da0, but problem still exists in master.

To reproduce:

1. Open landing page.
2. Resize window to be narrower than .container (1240px or less).
3. Observer the extra white space at the right side.

This is caused by the padding-left applied to .sponsor. Limiting
the size of .container fixes the problem.

uranusjr/pycontw2016,pycontw/pycontw2016,pycontw/pycontw2016,pycontw/pycontw2016,uranusjr/pycontw2016,uranusjr/pycontw2016,uranusjr/pycontw2016,pycontw/pycontw2016