Nodes - Added node type registration system

Nodes - Moved models and node logic into core
Nodes - Added node service that leverages DI

src/Artemis.VisualScripting/Nodes/CustomViewModels/StaticDoubleValueNodeCustomViewModel.cs

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+using Stylet;
+
+namespace Artemis.VisualScripting.Nodes.CustomViewModels
+{
+    public class StaticDoubleValueNodeCustomViewModel : PropertyChangedBase
+    {
+        private double _input;
+
+        public double Input
+        {
+            get => _input;
+            set => SetAndNotify(ref _input, value);
+        }
+    }
+}

src/Artemis.VisualScripting/Nodes/CustomViewModels/StaticIntegerValueNodeCustomViewModel.cs

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+using Stylet;
+
+namespace Artemis.VisualScripting.Nodes.CustomViewModels
+{
+    public class StaticIntegerValueNodeCustomViewModel : PropertyChangedBase
+    {
+        private int _input;
+
+        public int Input
+        {
+            get => _input;
+            set => SetAndNotify(ref _input, value);
+        }
+    }
+}

src/Artemis.VisualScripting/Nodes/CustomViewModels/StaticStringValueNodeCustomViewModel.cs

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+using Stylet;
+
+namespace Artemis.VisualScripting.Nodes.CustomViewModels
+{
+    public class StaticStringValueNodeCustomViewModel : PropertyChangedBase
+    {
+        private string _input;
+
+        public string Input
+        {
+            get => _input;
+            set => SetAndNotify(ref _input, value);
+        }
+    }
+}