Add simple blob viewers

app/models/blob_viewer/client_side.rb

+module BlobViewer
+  module ClientSide
+    extend ActiveSupport::Concern
+
+    included do
+      self.client_side = true
+      self.max_size = 10.megabytes
+      self.absolute_max_size = 50.megabytes
+    end
+  end
+end

app/models/blob_viewer/download.rb

+module BlobViewer
+  class Download < Base
+    include Simple
+    include ServerSide
+
+    self.partial_name = 'download'
+    self.text_based = false
+
+    def render_error(*)
+      nil
+    end
+  end
+end

app/models/blob_viewer/empty.rb

+module BlobViewer
+  class Empty < Base
+    include Simple
+    include ServerSide
+
+    self.partial_name = 'empty'
+    self.text_based = false
+  end
+end

app/models/blob_viewer/simple.rb

+module BlobViewer
+  module Simple
+    extend ActiveSupport::Concern
+
+    included do
+      self.type = :simple
+      self.switcher_icon = 'code'
+      self.switcher_title = 'source'
+    end
+  end
+end

app/models/blob_viewer/text.rb

+module BlobViewer
+  class Text < Base
+    include Simple
+    include ServerSide
+
+    self.partial_name = 'text'
+    self.text_based = true
+    self.max_size = 1.megabyte
+    self.absolute_max_size = 10.megabytes
+  end
+end

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

-- blob.load_all_data!(@repository)
-= render 'shared/file_highlight', blob: blob, repository: @repository

app/views/projects/blob/_download.html.haml → app/views/projects/blob/viewers/_download.html.haml

 .file-content.blob_file.blob-no-preview
   .center
-    = link_to namespace_project_raw_path(@project.namespace, @project, @id) do
+    = link_to blob_raw_url do
       %h1.light
-        %i.fa.fa-download
+        = icon('download')
       %h4
-        Download (#{number_to_human_size blob_size(blob)})
+        Download (#{number_to_human_size(viewer.blob.raw_size)})

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

+.file-content.code
+  .nothing-here-block
+    Empty file

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

+= render 'shared/file_highlight', blob: viewer.blob, repository: @repository