Rewrite class Router

[giuscris]

This PR rewrites and enhances the Router class adding some new features:

1. No more messy Router::add() method. Now Router::addRoute() only takes the route name and path. Everything else is chained:

$route = $router->addRoute('name', '/path/{param}/')
    ->action('Namespaced\\Controller\\ClassName@action')
    ->methods('GET', 'POST');

2. Optional route params:

$route = $router->addRoute('name', '/path/{param}/{optionalParam?}/');

3. Now routes can be imported from external files:

// /formwork/routes.php

return [
    'routes' => [
        'index' => [
            'path'   => '/',
            'action' => 'Formwork\\Controllers\\PageController@load'
        ],
        'index.pagination' => [
            'path'   => '/page/{paginationPage:num}/',
            'action' => 'Formwork\\Controllers\\PageController@load'
        ],
        'tag.pagination' => [
            'path'   => '/{page}/tag/{tagName:aln}/page/{paginationPage:num}/',
            'action' => 'Formwork\\Controllers\\PageController@load'
        ],
        'tag' => [
            'path'   => '/{page}/tag/{tagName:aln}/',
            'action' => 'Formwork\\Controllers\\PageController@load'
        ],
        'page.pagination' => [
            'path'   => '/{page}/page/{paginationPage:num}/',
            'action' => 'Formwork\\Controllers\\PageController@load'
        ],
        'page' => [
            'path'   => '/{page}/',
            'action' => 'Formwork\\Controllers\\PageController@load'
        ]
    ]
];

// /formwork/src/Formwork.php

// ...
    $this->router->loadFromFile($this->config()->get('routes.files.system'));
// ...