Fix figure spacing and center alignment

Currently there are two problems with figures:

1. There is no spacing after figures
2. Center alignment is ignored

This pull request fixes this. New styles are responsive and work correctly on smaller resolutions.

Example (before this change):

![selection_010](https://f.cloud.github.com/assets/125088/1888365/b9e62524-7a0c-11e3-8990-e0009a9a176c.png)

Example (after this change):

![selection_015](https://f.cloud.github.com/assets/125088/1888383/03bb3dd8-7a0d-11e3-9ac5-450c8c1a6fe5.png)