IS NULL criteria added to the `select` method in OCI connect

## find records with IS NULL criteria
Now you can use the `$I->seeInDatabase` method with `null` criterias

## load dump files with triggers
SQL commands should ends with `//` in the dump file
IF you want to load triggers too.
IF you do not want to load triggers you can use the `;` character
but in this case you need to change the $delimiter from `//` to `;`