Address review: zoom, drag, clearance and pitchDeg for voice tilt

- A zoom during a pivoting tilt now scales the range the tilt holds,
  as it already did for orbit, instead of being undone on the next
  frame while reporting success. The zoom limits no longer move a view
  the wrong way: a zoom in leaves a view closer than 80 m in place, and
  a zoom out leaves an orbit beyond 5,000 km where it is.
- A grab, touch or wheel on the map while a voice fly-to is in flight
  drops the motion queued behind it. Cesium lands the flight anyway,
  so the orbit or tilt would otherwise take the camera back. Chained
  fly-tos in one reply keep the earliest snapshot.
- A pivot tilt toward the horizon stops lowering the camera at 150 m
  above the pivot and tilts the rest in place, so a close view no
  longer ends inside tiles or a hillside.
- pitchDeg is an absolute angle. A direction that contradicts it is
  refused, judged from the pitch the swing starts at, and the tool
  description says so.

changelog.d/1520-voice-camera-tilt.md

@@ -2,4 +2,5 @@
   camera swings about the place under the crosshair, keeps its heading, and can
   tilt to a spoken angle ("tilt 45 degrees") or a default oblique view. A tilt,
   orbit, pan or rotate said with a fly-to ("fly to Paris and orbit it") now
-  waits for the flight to land (Manjunath, @manjunath22466, #1520).
+  waits for the flight to land, and is dropped if you move the map meanwhile
+  (Manjunath, @manjunath22466, #1520).