Make further properties multi-client and thread-safe

Move MovingPrimary, MovingSecondary, EarliestNonSlewingTime to
SharedResources, make all new properties thread-safe (atomic)
operations.

Meade.net/ThreadSafeBool.cs

@@ -0,0 +1,17 @@
+using System.Threading;
+
+namespace ASCOM.Meade.net
+{
+    public class ThreadSafeBool
+    {
+        private object _value;
+
+        public ThreadSafeBool(in bool value) => _value = value;
+
+        public void Set(in bool value) => Interlocked.Exchange(ref _value, value);
+
+        public static implicit operator ThreadSafeBool(in bool value) => new ThreadSafeBool(value);
+
+        public static implicit operator bool(ThreadSafeBool @this) => (bool)@this._value;
+    }
+}