Chrome can't executeScript on file:// URLs even though we have <all_urls> in manifest.json so on such pages we'll display a warning in the popup. This should only happen when Stylus is [re]enabled/reloaded.
* documentElement may be overwritten right after iframe was initialized with contentDocument.write() and due to this change being external it's not reported in our existing rewrite observer so we enqueue an additional check using setTimeout(0).
* match_about_blank in manifest.json is back
* iframes with src = about: or javascript: don't have a proper URL when our content script runs so we get the real URL from the parent window
* minor refactoring
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
* update state is shown in tooltips that fade out in 10 sec except for .update-problem and .can-update
* when updates are found a filtering option is revealed; when it's checked only entries with updates are shown; when all updates are installed the option automatically hides
Chrome doesn't garbage-collect (or even leaks) SVG <symbol> referenced via <use> so we'll embed the code directly on manage and popup pages where dozens/hundreds of svgs are displayed.
* restore the correct width of svg icons
* popup: use the standard formatting & SVG <symbol>
* popup .breadcrumbs hover highlight
* manage: black links, transitions; use <p> in #options; trim .homepage
* edit: move regexp tester info link to a template
* "Find styles" is a link so we make it one, just like in the popup.
* We have a dedicated global options UI so it makes no sense to subset only two of them on the manage page, moreover both options are unrelated to managing styles.
