[APT-10344] Use EncryptedSharedPreferences

 Encrypts widevine drm keys. The Android minSDK has been changed to version 23 in order to do this.

 Old DRM storage contents are migrated to the new one in SecureStorage

 The DRM storage backup files are excluded from syncing with Google Backup.

Armadillo/src/main/java/com/scribd/armadillo/encryption/SecureStorage.kt

@@ -89,12 +89,20 @@ internal class ArmadilloSecureStorage @Inject constructor(
         return download
     }
 
-    override fun getAllDrmDownloads(context: Context): Map<String, DrmDownload> =
-        legacyDrmStorage.all.keys.mapNotNull { key ->
-            legacyDrmStorage.getString(key, null)?.let { drmResult ->
-                key to drmResult.decodeToDrmDownload()
+    override fun getAllDrmDownloads(context: Context): Map<String, DrmDownload> {
+        val drmDownloads = secureDrmStorage.all.keys.mapNotNull { alias ->
+            secureDrmStorage.getString(alias, null)?.let { drmResult ->
+                alias to drmResult.decodeToDrmDownload()
             }
         }.toMap()
+        val legacyDownloads = legacyDrmStorage.all.keys.mapNotNull { alias ->
+            legacyDrmStorage.getString(alias, null)?.let { drmResult ->
+                alias to drmResult.decodeToDrmDownload()
+            }
+        }.toMap()
+
+        return drmDownloads.plus(legacyDownloads)
+    }
 
     override fun removeDrmDownload(context: Context, audioUrl: String, drmType: DrmType) {
         val alias = getDrmDownloadAlias(audioUrl, drmType)