Allow selection of fields with lowercased names as in propel1.

In Propel1 we had the ability to select fields with the lowercased names instead of the `phpName` (which is ucfirst).
```php
  ->select(array('title', 'bar'))
```
https://github.com/propelorm/Propel/blob/master/runtime/lib/query/ModelCriteria.php#L2088

Since `hasColumnByInsensitiveCase` has been removed I've adjusted the ModelCriteria in the way we can now define in Propel2 fields with lowercased names too.