Show maintenance mode error in notifications while uploading a file

# Conflicts:
#	build.gradle
#	res/values/strings.xml

src/main/java/com/owncloud/android/utils/ErrorMessageAdapter.java

@@ -84,6 +84,9 @@ public class ErrorMessageAdapter {
                 } else if (result.getCode() == ResultCode.INVALID_CHARACTER_DETECT_IN_SERVER) {
                     message = res.getString(R.string.filename_forbidden_charaters_from_server);
 
+                } else if (result.getCode() == ResultCode.MAINTENANCE_MODE) {
+                    message = res.getString(R.string.maintenance_mode);
+
                 } else {
                     message = String.format(
                             res.getString(R.string.uploader_upload_failed_content_single),