Trailing whitespaces removal
Documentation fixes:
- Cleanup in OAuth2StorageLaravel inline doc, some elements where refering to original PDO class
- Typo corrections
Error message mismatch fix
Added namespace declarations in interfaces to allow smooth inheritance if user extends OAuth2StorageLaravel to handle those grant types
Replaced 'echo' by 'die' at the end of OAuth2::grantAccessToken().
IT MAY BREAK BACKWARD COMPATIBILITY if people did something in their controller after calling the function.
However, it's more consistent with the other output functions (e.g. Oauth2::finishClientAuthorization) and as the library handles the entire response (headers and body) it allows to keep its process internal.
Otherwise if user does not use a die() or exit() explicitely in its controller, Laravel will for example overwrite the 'Content-Type' header from 'application/json' to 'text/html'
Really no reason to hardcode a maximal limit for client_id length
Adaptated the bundle to allow fine-tuning without altering bundle files.
- DB tables names can be configured in a configuration file
- Migrations have been updated to be configurable: they use the dynamic tables names and details of tables structures are externalized in a subdirectory that can be overwritten through the configuration file
- Client migration name has been changed so that it's the first to be executed. As clients table is referenced by others, it allows developer to add foreign keys constraints on client_id columns
- A .gitignore file has been added to ignore customizable elements: configuration file, custom migration details and classes overwritten by developer
Documentation has been updated accordingly.

If no specific configuration is applied, database structure will be the same as before, with a few exceptions:
- client_secret has been set to 60 chars length in the clients tables: no need more, as the hashes generated by the bundle are that length.
- redirect_uri length was sometimes 200, sometimes 255. It has been harmonized to 255.
- scope length has been enlarged to 255
Added a placeholder method for exception handling, as the class calls it but the method itself was gone like Keyser Söze.
Added a few more namespaces declarations forgotten in the first pass
- Deletion of unnecessary namespaces in migrations that can be annoying for developers having extended the core Config class
- Deletion of "\" prefixes in use declarations in Laravel storage class, to conform with PHP guidelines (see http://php.net/manual/en/language.namespaces.importing.php)