Make further properties multi-client and thread-safe

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

Meade.net/ThreadSafeEnum.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Threading;
+
+namespace ASCOM.Meade.net
+{
+    public class ThreadSafeEnum<T>
+        where T: struct, Enum
+    {
+        private long _value;
+
+        public ThreadSafeEnum(T value) => _value = EnumToLong(value);
+
+        public void Set(T value) => Interlocked.Exchange(ref _value, EnumToLong(value));
+
+        private static long EnumToLong(T value) => Convert.ToInt64(value);
+
+        public static implicit operator ThreadSafeEnum<T>(T value) => new ThreadSafeEnum<T>(value);
+
+        public static implicit operator T(ThreadSafeEnum<T> @this) => (T) Enum.ToObject(typeof(T), Interlocked.Read(ref @this._value));
+    }
+}