make some more classes and methods internal (#3353)

* WIP public->internal

* DemoStore back to public, internal on Timers

com.unity.ml-agents/Runtime/ActionMasker.cs

 
         readonly BrainParameters m_BrainParameters;
 
-        public ActionMasker(BrainParameters brainParameters)
+        internal ActionMasker(BrainParameters brainParameters)
         {
             m_BrainParameters = brainParameters;
         }

com.unity.ml-agents/Runtime/ICommunicator.cs

 
 namespace MLAgents
 {
-    public struct CommunicatorInitParameters
+    internal struct CommunicatorInitParameters
     {
         /// <summary>
         /// Port to listen for connections on.
         /// </summary>
         public string version;
     }
-    public struct UnityRLInitParameters
+    internal struct UnityRLInitParameters
     {
         /// <summary>
         /// An RNG seed sent from the python process to Unity.
-    public struct UnityRLInputParameters
+    internal struct UnityRLInputParameters
     {
         /// <summary>
         /// Boolean sent back from python to indicate whether or not training is happening.
     /// <summary>
     /// Delegate for handling quite events sent back from the communicator.
     /// </summary>
-    public delegate void QuitCommandHandler();
+    internal delegate void QuitCommandHandler();
-    public delegate void ResetCommandHandler();
+    internal delegate void ResetCommandHandler();
-    public delegate void RLInputReceivedHandler(UnityRLInputParameters inputParams);
+    internal delegate void RLInputReceivedHandler(UnityRLInputParameters inputParams);
 
     /**
     This is the interface of the Communicators.

com.unity.ml-agents/Runtime/Policy/RemotePolicy.cs

         int m_AgentId;
         string m_FullyQualifiedBehaviorName;
 
-        protected ICommunicator m_Communicator;
+        internal ICommunicator m_Communicator;
 
         /// <inheritdoc />
         public RemotePolicy(

com.unity.ml-agents/Runtime/Sensor/Observation.cs

 
 namespace MLAgents.Sensor
 {
-    public struct Observation
+    internal struct Observation
     {
         /// <summary>
         /// The compressed sensor data. Assumed to be non-null if CompressionType != CompressionType.None

com.unity.ml-agents/Runtime/Sensor/SensorShapeValidator.cs

 
 namespace MLAgents.Sensor
 {
-    public class SensorShapeValidator
+    internal class SensorShapeValidator
     {
         private List<int[]> m_SensorShapes;
 

com.unity.ml-agents/Runtime/Sensor/StackingSensor.cs

     ///   |  t = now - 3  |  t = now -3  |  t = now - 2  |  t = now  |
     /// Internally, a circular buffer of arrays is used. The m_CurrentIndex represents the most recent observation.
     /// </summary>
-    public class StackingSensor : ISensor
+    internal class StackingSensor : ISensor
     {
         /// <summary>
         /// The wrapped sensor.

com.unity.ml-agents/Runtime/Timer.cs

 namespace MLAgents
 {
     [DataContract]
-    public class TimerNode
+    internal class TimerNode
     {
         static string s_Separator = ".";
         static double s_TicksToSeconds = 1e-7; // 100 ns per tick
     /// Tracks the most recent value of a metric. This is analogous to gauges in statsd.
     /// </summary>
     [DataContract]
-    public class GaugeNode
+    internal class GaugeNode
     {
         const float k_SmoothingFactor = .25f; // weight for exponential moving average.
 
             get { return k_Instance; }
         }
 
-        public TimerNode RootNode
+        internal TimerNode RootNode
         {
             get { return m_RootNode; }
         }
         /// Potentially slow so call sparingly.
         /// </summary>
         /// <returns></returns>
-        public string DebugGetTimerString()
+        internal string DebugGetTimerString()
         {
             return m_RootNode.DebugGetTimerString();
         }