Revert "Popout inbox"

This reverts commit 31e7d285e3.

This seemed like a nice feature, but the popup bubble isn't very
conducive to nontrivial user inputs, e.g. file inputs.

Fixes #211

js/background.js

@@ -65,6 +65,8 @@
             });
         });
 
+        extension.browserAction(window.openInbox);
+
         // refresh views
         var views = extension.windows.getViews();
         for (var i = 0; i < views.length; ++i) {