Add layout to digests

[spodlecki]

Adding capability to get digest from <%= render layout: "_TEMPLATE_" do %>

Added tests

-- This current functionality is available in the Rails 4 version, but some of our older projects are still a bit aways from getting updated. The do block still gives problems with HAML, but that's a whole "new" problem

-- Only actual code change is adding layout to RegEx, the rest is from tests.