Fix aliases on related entities.

[romaninsh]

When related entity relies on the same table it is possible to run into problem when SQL is confused about which table to use.

select
   name, 
  (select name from item 
   where item.parent_id = item.id
  ) parent_name
from item

To avoid this problem this PR introduces use of aliases in related entities. The related table alias does not have to be passed and it will be automatically deducted from field:

With this patch recursive models produce queries like this:

select
    `pp`.`id`,`pp`.`name`,`pp`.`age`,`pp_i`.`parent_item_id`,
    (select `parent`.`name` 
     from `item` `parent`
     left join `item2` as `parent_i` on `parent_i`.`item_id` = `parent`.`id` 
     where `parent`.`id` = `pp_i`.`parent_item_id`
     ) `parent_item`,
    (select sum(`child`.`age`) from `item` `child`
     left join `item2` as `child_i` on `child_i`.`item_id` = `child`.`id` 
     where `child_i`.`parent_item_id` = `pp`.`id`
    ) `child_age`,`pp`.`id` `_i` 
from `item` `pp`left join `item2` as `pp_i` on `pp_i`.`item_id` = `pp`.`id`

[skondakov]

Seems good to me! I've also tested the examples in the section.