Create a simple dialogue authoring system, tied into our items (#10)

- Editor dialogue graph
- Asset importer for processing the graph into runtime data
- DialogueComponent that steers the dialogue interactions
- DialogueCanbas with a scalable speech bubble to display everything
- Brief README overview of the system

Co-authored-by: AlexanderT <alexander@foolhardyhorizons.com>
Co-authored-by: Michal Pikulski <michal.a.pikulski@gmail.com>
Reviewed-on: #10

Assets/Editor/Dialogue/DialogueGraph.cs

@@ -0,0 +1,20 @@
+using System;
+using UnityEngine;
+using UnityEditor;
+using Unity.GraphToolkit.Editor;
+
+namespace Editor.Dialogue
+{
+    [Serializable]
+    [Graph(AssetExtension)]
+    public class DialogueGraph : Graph
+    {
+        public const string AssetExtension = "dialoguegraph";
+        
+        [MenuItem("Assets/Create/Dialogue Graph", false)]
+        private static void CreateAssetFile()
+        {
+            GraphDatabase.PromptInProjectBrowserToCreateNewAsset<DialogueGraph>();
+        }
+    }
+}