docket: rename to Grid

System was extremely confusing because %base is also referred to as
System.  Also allow it to show up in the app preferences list, so that
you can change its OTA source.

desk/desk.docket-0

@@ -1,4 +1,4 @@
-:~  title+'System'
+:~  title+'Grid'
     info+'An app launcher for Urbit.'
     color+0xee.5432
     glob-http+['https://bootstrap.urbit.org/glob-0v1.tqd6t.ggt8r.roheb.l3bvq.sbm6d.glob' 0v1.tqd6t.ggt8r.roheb.l3bvq.sbm6d]

ui/src/preferences/SystemPreferences.tsx

@@ -72,7 +72,6 @@ export const SystemPreferences = (
   const { systemBlocked } = useSystemUpdate();
   const charges = useCharges();
   const filteredCharges = Object.values(charges)
-    .filter((charge) => charge.desk !== window.desk)
     .filter((charge) => charge.desk !== 'landscape');
   const isMobile = useMedia('(max-width: 639px)');
   const settingsPath = isMobile ? `${match.url}/:submenu` : '/';