Use photos directory to store photos.

Currently the sample demonstrates storing images in the root
of the external storage. It may be useful to demonstrate having
a directory where a developer can store their files.

Change-Id: I5c51df40c630271f763315f6a694f01e8a4b9f5c

storage/app/src/main/java/com/google/firebase/quickstart/firebasestorage/MainActivity.java

@@ -232,9 +232,13 @@ private void launchCamera() {
         }
 
         // Choose file storage location, must be listed in res/xml/file_paths.xml
-        File file = new File(Environment.getExternalStorageDirectory(),
-                UUID.randomUUID().toString() + ".jpg");
+        File dir = new File(Environment.getExternalStorageDirectory() + "/photos");
+        File file = new File(dir, UUID.randomUUID().toString() + ".jpg");
         try {
+            // Create directory if it does not exist.
+            if (!dir.exists()) {
+                dir.mkdir();
+            }
             boolean created = file.createNewFile();
             Log.d(TAG, "file.createNewFile:" + file.getAbsolutePath() + ":" + created);
         } catch (IOException e) {

storage/app/src/main/res/xml/file_paths.xml

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <paths>
-    <external-path name="external" path="." />
+    <external-path name="external" path="photos/" />
 </paths>