Add artifacts browser

This implementation makes it possible to browse artifacts, it
depends on artifacts metadata.

app/controllers/projects/artifacts_controller.rb

@@ -15,10 +15,8 @@ class Projects::ArtifactsController < Projects::ApplicationController
   end
 
   def browse
-    path = params[:path].to_s
-    @paths = artifacts_metadata.map do |_artifact_file|
-      Gitlab::StringPath.new(path, artifacts_metadata)
-    end
+    current_path = params[:path] ? "./#{params[:path]}/" : './'
+    @path = Gitlab::StringPath.new(current_path, artifacts_metadata)
   end
 
   private

app/views/projects/artifacts/_tree_directory.html.haml

+%tr{ class: 'tree-item' }
+  %td.tree-item-file-name
+    = tree_icon('folder', '755', directory.basename)
+    %span.str-truncated
+      = link_to directory.basename, browse_namespace_project_build_artifacts_path(@project.namespace, @project, @build, path: directory.path)  

app/views/projects/artifacts/_tree_file.html.haml

+%tr{ class: 'tree-item' }
+  %td.tree-item-file-name
+    = tree_icon('file', '664', file.basename)
+    %span.str-truncated
+      = file.basename

app/views/projects/artifacts/browse.html.haml

 - page_title "#{@build.name} (##{@build.id})", 'Build artifacts'
 - header_title project_title(@project, "Build artifacts", namespace_project_build_path(@project.namespace, @project, @build))
 
-= @metadata.inspect
+%table.table.table-hover
+  = render partial: 'tree_directory', collection: @path.directories, as: :directory
+  = render partial: 'tree_file', collection: @path.files, as: :file