Need to get rails to precompile the prerender assets

The configuration / generator script needs to add this line to
```ruby
Rails.application.config.assets.precompile += %w( hyperstack-prerender-loader.js )
```
to the `config/initializers/assets.rb` file.

Work around is to add this file when turning pre-rendering on.

Might be nice if this could automatically be added if pre-rendering is on.