Draw no buoy for a virtual aid to navigation

A virtual aid (AIS message 21's VirtualAtoN flag) is a mark broadcast
where nothing physical stands, so drawing it as a buoy showed a mark
that is not there. The vessel source record now carries `virtual`
(false unless a source says true; any source may set it), AISStream
sets it from VirtualAtoN, and the vessel layer keeps such an aid's
disc: vesselModelSpec returns null for it and the layer gathers no
model item for it. Its card, selected card and readout add VIRTUAL
after its kind.

src/i18n/locales/he.json

@@ -1150,6 +1150,7 @@
   "{type}  SPD: {speed}  HDG: {heading}": "{type}  SPD: {speed}  HDG: {heading}",
   "VESSEL": "אונייה",
   "AID TO NAVIGATION": "עזר ניווט",
+  "VIRTUAL": "וירטואלי",
   "{speed}KT": "{speed} קשר",
   "{heading}DEG": "{heading}°",
   "POS: LIVE": "POS: חי",