To prevent cross-page leaks we need to create/copy prefs and cachedStyles inside the background page context.
* storage.js is now used only in the background page
* messaging.js now contains less bg-specific methods and more common methods. Added saveStyleSafe, deleteStyleSafe which automatically invoke onRuntimeMessage of the current page or just handleUpdate/handleDelete when notify:false
* prefs.js with 'prefs' for background and UI pages: separate objects because a UI page may load before the background page and it can read prefs from localStorage/sync/defaults
* [x] show badge with active styles count
* [x] styles on top in the popup
* Simplify since we use a persistent background page so it's always there for us
Popup:
* Enforce 200-800px range for the popup width option
Manage:
* faster search via cachedStyles.byId
* faster restoration of search results on history nav
* style name is clickable and opens the editor
* animated highlight of style element on update/add/save
* expandable extra applies-to targets
* remember scroll position on normal history navigation
* boz-sizing in #header, also in editor
* applies-to targets use structured markup
* get*Tab*, enableStyle and deleteStyle are promisified
