Allow setting content for resolutions

When reading conflicts:

1. Add a `type` field. `text` works as before, and has `sections`;
   `text-editor` is a file with ambiguous conflict markers that can only
   be resolved in an editor.
2. Add a `content_path` field pointing to a JSON representation of the
   file's content for a single file.
3. Hitting `content_path` returns a similar datastructure to the `file`,
   but without the `content_path` and `sections` fields, and with a
   `content` field containing the full contents of the file (with
   conflict markers).

When writing conflicts:

1. Instead of `sections` being at the top level, they are now in a
   `files` array. This matches the read format better.
2. The `files` array contains file hashes, each of which must contain:
   a. `new_path`
   b. `old_path`
   c. EITHER `sections` (which works as before) or `content` (with the
      full content of the resolved file).

1 files changed, 6 insertions, 1 deletions

diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index b3455e04c29..bf37421771f 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -114,7 +114,12 @@ class ApplicationController < ActionController::Base
   end
 
   def render_404
-    render file: Rails.root.join("public", "404"), layout: false, status: "404"
+    respond_to do |format|
+      format.json { head :not_found }
+      format.any do
+        render file: Rails.root.join("public", "404"), layout: false, status: "404"
+      end
+    end
   end
 
   def no_cache_headers