Common reorg (#8025)

* Re-organize common folder

* fix: Correct paths in tests

* fix: move new content to proper folder

* chore: Move audio folder to assets

* Move sprites to sprites assets directory

* Move css sprites to assets directory

* Split out readmes for common code and sprites

* Move images to assets directory

* Move destinatin of shared browserified file

* remove unused file

* move compiled js to client-old

* Fix karma tests

* fix: Correct paths for sprites

website/common/script/content/gear/back.js

@@ -0,0 +1,13 @@
+import {back as baseBack} from './sets/base';
+
+import {back as mysteryBack} from './sets/mystery';
+import {back as specialBack} from './sets/special';
+
+let back = {
+  base: baseBack,
+  mystery: mysteryBack,
+  special: specialBack,
+};
+
+module.exports = back;
+