Add a Login/Logout toggle item in WordPress navigation menu. Source: http://rezzz.com/add-login-and-logout-to-your-wordpress-menu/

add-loginout-nav-item.php

<?php

//* Add a Login/Logout toggle item in WordPress navigation menu
add_filter('wp_nav_menu_items', 'customprefix_add_loginout_navitem', 10, 2);
function customprefix_add_loginout_navitem($items, $args) {
    if ($args->theme_location == 'primary') {
         // Replace "primary" with your theme's menu name
        if (!(is_user_logged_in())) {
            $login_item = '<li class="menu-item login-menu-item"><a itemprop="url" href="/wp-login.php" rel="nofollow">Log in</a></li>';
        } 
        else {
            $login_item = '<li class="menu-item logout-menu-item">' . wp_loginout($_SERVER['REQUEST_URI'], false) . '</li>';
        }
        $items.= $login_item;
    }
    return $items;
}

redirect-users-after-login.php

<?php

/**
 * Redirect admins to WordPress Dashboard and other users to site's homepage after a successful login
 * https://codex.wordpress.org/Plugin_API/Filter_Reference/login_redirect
 *
 * @param string $redirect_to URL to redirect to
 * @param string $request URL the user is coming from
 * @param object $user Logged user's data
 * @return string
 */
add_filter( 'login_redirect', 'customprefix_login_redirect', 10, 3 );
function customprefix_login_redirect( $redirect_to, $request, $user ) {
    //is there a user to check?
    global $user;
    if ( isset( $user->roles ) && is_array( $user->roles ) ) {
        //check for admins
        if ( in_array( 'administrator', $user->roles ) ) {
            // redirect them to the default place
            return $redirect_to;
        } else {
            return home_url();
        }
    } else {
        return $redirect_to;
    }
}

redirect-users-after-logout.php

<?php

//* Redirect all users to site's homepage after logout
add_filter( 'logout_redirect', create_function( '$url,$query,$user', 'return home_url();' ), 10, 3 );