Refactored database, refactored config file, corrected login redirection

Moved database function in class "Database";
Corrected database-using webpages accordingly;
Moved config file from PHP to JSON with more config variables;
Corrected login page redirection on wrong username or password.

js/login.js

@@ -1,4 +1,4 @@
-function login() {
+function login ( ) {
     var username = document.getElementById ( "form-username" ).value;
     var password = document.getElementById ( "form-password" ).value;
     password = SHA512 ( password );
@@ -13,7 +13,7 @@ function login() {
                     window.location.href = script_name;
                 }
                 else {
-                    document.getElementById ( "responsetext" ).innerHTML = response [ 'error_message' ];
+                    console.log ( response [ 'error_message' ] );
                 }
             }
         else {
@@ -26,3 +26,11 @@ function login() {
     data.append('password', password);
     xhr.send( data );
 }
+
+$(function ( ) {
+    $( '.form-group input' ).keyup( function ( e ) {
+        if ( e.keyCode == 13 ) {
+            login();
+        }
+    });
+});