Refactor extension to webpack

This change is the biggest in the history of the project. The entire
project has been refactored so it is built with webpack.

This involves:
- Creating webpack and npm config files.
- Fixing some bugs in the code due to the fact that webpack uses strict
mode.
- Merging some pieces of code which were shared throughout the codebase
(not exhaustive, more work should be done in this direction).
- Splitting the console_inject.js file into separate files (it had 1000+
lines).
- Adapting all the build-related files (Makefile, bash scripts, etc.)
- Changing the docs to explain the new build process.
- Changing the Zuul playbook/roles to adapt to the new build process.

Change-Id: I16476d47825461c3a318b3f1a1eddb06b2df2e89
diff --git a/src/background.js b/src/background.js
index 8d0f411..15f62b9 100644
--- a/src/background.js
+++ b/src/background.js
@@ -1,4 +1,5 @@
 // IMPORTANT: keep this file in sync with sw.js
+import {cleanUpOptions} from './common/optionsUtils.js'
 
 // When the extension gets updated, set new options to their default value.
 chrome.runtime.onInstalled.addListener(function(details) {