New Database API

This pull request introduce an improved Database API, in a Laravel-esque style, including a QueryBuilder and a simple but powerful Model, everything living in the namespace '\Database' from isolation reasons.

To note that this new Database API doesn't replace any of existent classes, the actual Core\Model and Helpers\Database remaining untouched. Then an end-user can choose which Database API use in his application, with the only condition to not use both of them simultaneous, thing which will duplicate the Database connections.

Then new API is structured on three levels.

First one of the levels, being a Database Connection, built on top of PDO, which is available both via getting an instance:

use Database\Connection;

$db = Connnection::getInstance();

$prefix = $db->getTablePrefix();

$data = $db->select("SELECT * FROM {$prefix}users");

and via a Facade which permit commands like:

use DB;

$prefix = DB::getTablePrefix();

$data = DB::select("SELECT * FROM {$prefix}users");

Commands for insert/update/delete are available.

To note that the Database\Connection fetch the data into objects or array of objects.

The second level is represented by a very simple but powerful QueryBuilder, which permits commands like:

use DB;

$users = DB::table('users')->get();

$users = DB::table('users')->where('role', '=', 'admin')->get();

The third level is represented by a simple, yet powerful, Model, which use the Database\Connection instead of Helpers\Database. It is recommended way to use the new Database API, and can have a structure like:

namespace App\Models;

use Database\Model;

class Users extends Model
{
    protected $table = 'users';

    protected $primaryKey = 'userId';

    public function __construct()
    {
        parent::__construct();
    }
}

To note the two protected variables, which specify the Table name and Primary Key, which are mandatory to be configured, specially the Table name, the second one defaulting to 'id'.

A Database\Model is similar as usage with the Core\Model, but have the ability to transparently use the QueryBuilder methods, then permitting command like this:

use App\Models\Users;

$model = new Users();

$users = $model->where('role', '=', 'admin')->get();

Also, the Database\Model offer associated QueryBuilder instances, as following:

use App\Models\Users;

$model = new Users();

$query = $model->newQuery();

$users = $query->where('role', '=', 'admin')->get();