Adding more ActiveRecord like search methods

I plan to use https://github.com/moger777/missingly to create some better search methods that would react to your added fields.

I would be looking at the end result being:

```ruby
Adauth::AdObjects::User.find_by_login("arcath")
Adauth::AdObjects::Group.find_by_name("a group")
```

With the ability to order aswell

```ruby
Adauth::AdObjects::User.all.order(:login)
```