Fixed while traveling to heuruko

Move SCSS generators and default templates from Rails to the Sass Railtie (d435726312601edb3ba6f97b34f562221f72c1f8).

* Sass gem registers a compressor
* Sass gem registers generators for assets and scaffold
* Create a default stylesheet_engine ("css") for apps that remove the Sass gem

Change compressor API so that plugins can register default compressors for their stylesheet or JS engines and still allow the user to turn off compression

Replace references to ActiveSupport::SecureRandom with just SecureRandom, and require 'securerandom' from the stdlib when active support is required.

Also, no need to include dependencies in AS::Concerns inside included blocks.

Revert "Take into account time spent in AR even if a redirect occurs or if it is after the render" because it's causing test failures about missing db_during_render.

This reverts commit 60b55bac.

Sprocket was trying to look for these two things:

* `Rails::VERSION::STRING`
* `.initializer(str)` in `Rails::Engine`

This commit added require to version.rb into Abstract Unit, and mocking the `Rails::Engine.initializer` in `sprockets_helper_test.rb`

- exclude Rack::Test::UploadedFile to pass existing tests. Are there any
  other types we're missing?