[gallery] Fix Gallery and Console

- Fix brython.css styles.
- Fix Gallery and Console styles and markup.
- Fix PEP8 / Lint on the Python. 
- Remove unneeded empty trailing white spaces.
- Pages got the same base `<head>` tags.
- No images, just CSS.
- Remove obsolete readme.txt in favor of readme.md


![gallery_styles](https://cloud.githubusercontent.com/assets/1189414/4604435/1e8317d6-519d-11e4-9820-cc98a666e7c8.jpg)


:octocat: