Move Mass Storage app to firmware repo

applications/system/mass_storage/application.fam

@@ -0,0 +1,16 @@
+App(
+    appid="mass_storage",
+    name="Mass Storage",
+    apptype=FlipperAppType.EXTERNAL,
+    entry_point="mass_storage_app",
+    requires=[
+        "gui",
+        "dialogs",
+    ],
+    stack_size=2 * 1024,
+    fap_description="Implements a mass storage device over USB for disk images",
+    fap_version="1.3",
+    fap_icon="assets/floppydisk_10px.png",
+    fap_icon_assets="assets",
+    fap_category="USB",
+)