fix(bundle): align the web debug toolbar item with the Symfony core styles

The item label used `sf-toolbar-status`, which renders it on a grey badge
instead of the plain value styling of the core items. It now uses
`sf-toolbar-value`.

The icon was a base64 PNG export of the jwt.io logo, on an opaque white
background and with fixed colours, which looked out of place next to the
monochrome core icons. It is replaced by the official jwt.io SVG, normalised
to the 24x24 grid used by the WebProfilerBundle icons and painted with
`currentColor`, so the mark follows the toolbar foreground in both the light
and the dark theme -- including the two branches that jwt.io itself renders
white or black depending on the background.

Fixes #663

Author: Spomky