Add new views and styles for music application

- Created new CSS files for styling the application, including home.css and style.css.
- Implemented 403 and 404 error views with appropriate messages and navigation.
- Developed a dump view to display deleted elements with restoration options.
- Enhanced home view to include music search functionality and display results.
- Added listplay view for managing music playlists, including creation and deletion options.
- Implemented loadmusic view for uploading new music with necessary fields.
- Created login and register views for user authentication.
- Developed sound view to display individual music tracks with playback controls and options for liking and deleting.
- Updated menu view to include navigation links based on user authentication status.

request/post/register.post.php

@@ -0,0 +1,24 @@
+<?php
+
+$newUser = false;
+if (isset($_POST['username']) && isset($_POST['password']) && isset($_POST['rpassword'])) {
+    if (!$user->exists($_POST['username'])) {
+        if (strpos('_' . $_POST['username'], ' ') <= 0) {
+            if ($_POST['password'] == $_POST['rpassword']) {
+                $user->newUser($_POST);
+                $message = 'Usuario creado con exito!';
+                $newUser = true;
+            } else {
+                $message = "Las claves no coinciden.";
+            }
+        } else {
+            $message = "El nombre de usuario <b>\"{$_POST['username']}\"</b> no debe tener espacios.";
+        }
+    } else {
+        $message = "El usuario <b>{$_POST['username']}</b> existe.";
+    }
+}
+
+header("location: ./?view=$view&newuser=$newUser&message=$message");
+
+?>