Flatten threads: fix for application/json+protobuf responses

When a new message is created in a thread, the thread itself is
reloaded, but via an application/json+protobuf request (array-like data)
instead of a regular text/plain request (object-like data). Since the
code didn't work well for these types of requests, the thread didn't
fully load.

This CL fixes this issue by correctly handling application/json+protobuf
responses in the response modifiers.

An issue with the read-only interceptors has also been fixed, and tests
have been added to ensure that the array-like to object-like and
viceversa transformation functions work properly.

Bug: twpowertools:153
Change-Id: If6cd5adc67d676bf36986f325e791124fa71da51
diff --git a/.babelrc b/.babelrc
new file mode 100644
index 0000000..7521eb0
--- /dev/null
+++ b/.babelrc
@@ -0,0 +1,7 @@
+  "env": {
+    "test": {
+      "plugins": ["@babel/plugin-transform-modules-commonjs"]
+    }
+  }