react-express-mongodb: rename server to backend

The goal here is to keep the same structure than the other examples.
Also, considering that it has a "frontend" folder, the equivalent for
the server should be "backend".

Signed-off-by: Jérémie Drouet <jeremie.drouet@gmail.com>

react-express-mongodb/server/config/messages.js

@@ -1,62 +0,0 @@
-module.exports = {
-    AUTHENTICATION_FAILED: {
-        code: 400,
-        message: 'Authentication failed. Please login with valid credentials.',
-        success: false,
-    },
-    SUCCESSFUL_LOGIN: {
-        code: 200,
-        message: 'Successfully logged in',
-        success: true,
-    },
-    INTERNAL_SERVER_ERROR: {
-        code: 500,
-        message: 'Something unexpected happened',
-        success: false,
-    },
-    UNAUTHORIZED: {
-        code: 401,
-        message: 'You session is expired. Please login again',
-        success: false,
-    },
-    SUCCESSFUL_DELETE: {
-        code: 200,
-        message: 'Successfully deleted',
-        success: true,
-    },
-    SUCCESSFUL_UPDATE: {
-        code: 200,
-        message: 'Updated successfully',
-        success: true,
-    },
-    SUCCESSFUL: {
-        code: 200,
-        success: true,
-        message: 'Successfully completed',
-    },
-    NOT_FOUND: {
-        code: 404,
-        success: true,
-        message: 'Requested API not found',
-    },
-    ALREADY_EXIST: {
-        code: 200,
-        success: true,
-        message: 'Already exists',
-    },
-    FORBIDDEN: {
-        code: 403,
-        message: 'You are not authorized to complete this action',
-        success: false,
-    },
-    BAD_REQUEST: {
-        code: 400,
-        message: 'Bad request. Please try again with valid parameters',
-        success: false,
-    },
-    IN_COMPLETE_REQUEST: {
-        code: 422,
-        message: 'Required parameter missing',
-        success: false,
-    },
-};