Use blob viewers for snippets

app/assets/javascripts/blob/viewer/index.js

app/assets/javascripts/dispatcher.js

app/assets/javascripts/line_highlighter.js

app/controllers/concerns/renders_blob.rb

app/controllers/projects/blob_controller.rb

app/controllers/projects/snippets_controller.rb

app/controllers/snippets_controller.rb

app/helpers/blob_helper.rb

app/models/snippet.rb

app/models/snippet_blob.rb

app/views/projects/blob/_header.html.haml

app/views/projects/blob/viewers/_markup.html.haml

app/views/projects/snippets/show.html.haml

app/views/search/results/_snippet_blob.html.haml

app/views/shared/snippets/_blob.html.haml

app/views/snippets/show.html.haml

features/project/snippets.feature

features/snippets/snippets.feature

features/steps/project/snippets.rb

features/steps/snippets/snippets.rb