recognise files with "image" extension as disk images

Mini vMac/AppDelegate.m

@@ -225,7 +225,7 @@ static NSObject<Emulator> *sharedEmulator = nil;
 }
 
 - (NSArray<NSString *> *)diskImageExtensions {
-    return @[@"dsk", @"img", @"dc42", @"diskcopy42"];
+    return @[@"dsk", @"img", @"dc42", @"diskcopy42", @"image"];
 }
 
 - (NSString *)documentsPath {

Mini vMac/Info.plist

@@ -123,6 +123,7 @@
 				<array>
 					<string>img</string>
 					<string>dsk</string>
+					<string>image</string>
 				</array>
 			</dict>
 		</dict>