Reusing of database and multiple connections

Changed a little bit database class. You don't have to change any code in model or anywhere else. This pull request allows to reuse database, preventing of duplicating connections and multiple connections by passing array with information, example:

```php
new database(array (
'type' => 'mysql',
'host' => 'mysql.host.com',
'name' => 'my_db',
'user' => 'flashlazer',
'password' => 'YourSecretPassword'
));
```

However, I would write it using [Multiton](http://en.wikipedia.org/wiki/Multiton_pattern) pattern, but @andre2 didn't really liked it much :smile: