CU-868f2gyjp: Add Sample Video For Editor Testing (#207)

### TL;DR

Added sample video and content for editor mode in the Video content type.

### What changed?

- Updated the `GetFullVideoFilePath()` method in the `Video` class to return a sample video path when running in the Unity Editor
- Added a check for `Application.isEditor` that returns a predefined sample video path
- Added `UnityEngine` namespace import to support the `Application` class
- Updated the Files.zip binary file to add a sample video

### Sample Video

The sample video is Big Buck Bunny; likely one of the most commonly used videos for testing purposes. Created by Blender in 2008 - it's open license, high quality and family friendly content was setup specifically for this use case. For more details see here: https://peach.blender.org/about/

Author: nic-mxr

Assets/MXR.SDK/Files.zip

@@ -3,6 +3,7 @@
 
 using Newtonsoft.Json;
 using Newtonsoft.Json.Converters;
+using UnityEngine;
 
 namespace MXR.SDK {
     /// <summary>
@@ -157,6 +158,10 @@ public class Video : Content {
         public string videoPath;
 
         public string GetFullVideoFilePath() {
+            if (Application.isEditor) {
+                return MXRStorage.GetFullPath("/MightyImmersion/videos/sample.mp4");
+            }
+            
             if (string.IsNullOrEmpty(videoPath)) {
                 return null;
             }
@@ -255,4 +260,4 @@ public class RuntimeApp : Content {
         /// </summary>
         public long expirationTimestamp;
     }
-}
+}