This module provides an abstract model to manage SQL Select requests on
database. It is not usefull for itself. You can see an exemple of
implementation in the 'sql_export' module. (same repository).

## Implemented features

- Add some restrictions in the sql request:  
  - you can only read datas. No update, deletion or creation are
    possible.
  - some tables are not allowed, because they could contains clear
    password or keys. For the time being ('ir_config_parameter').

- The request can be in a 'draft' or a 'SQL Valid' status. To be valid,
  the request has to be cleaned, checked and tested. All of this
  operations can be disabled in the inherited modules.

- This module two new groups:  
  - SQL Request / User : Can see all the sql requests by default and
    execute them, if they are valid.
  - SQL Request / Manager : has full access on sql requests.