layout: kill padding-right of .content

This causes layout issues in FF30 under Linux, so drop it.
Gemfile: add autoprefixer

Autoprefixer is a tool to parse CSS and add vendor prefixes to CSS rules
using values from the Can I Use. This gem provides Ruby and Ruby on Rails
integration with this JavaScript tool.
TextBlock: return a dummy object if lookup has failed

This eases the user side of this class, as we can rely to get back something
from the method, regardless if the TextBlock actually exists in the
database.
index: render using TextBlocks
Remove 'static' layout in favor of using yields.