Refactor theme handling so that it is unified via a helper method

lib/screenshot.rb

@@ -20,10 +20,7 @@ class Screenshot
   end
 
   def initialize(theme)
-    @theme = OpenStruct.new(theme.merge(
-      slug: theme[:name].parameterize.underscore,
-      digest: Digest::MD5.new.hexdigest(theme[:colors])
-    ))
+    @theme = theme
   end
 
   def generate_theme_image

lib/screenshot_generator.rb

@@ -7,10 +7,11 @@ class ScreenshotGenerator < ::Middleman::Extension
     super
     app.before_build do |builder|
       Screenshot.prepare
-      data = YAML.load_file('data/themes.yml')
-      data.each do |theme|
+
+      themes.each do |theme|
         Screenshot.new(theme).generate_theme_image
       end
+
       puts "Hello World"
       # builder.run './my_deploy_script.sh'
     end