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

#### find records with IS NULL criteria (copied from PostgreSql.php)
Now you can use the `$I->seeInDatabase` method - and other methods with db usage - 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 `;`

in Oracle DBs for autoincrementing the ID value you need to use a trigger. So in the most of the cases triggers are exists. Thats why I set the default delimiter to `//` instead of `;`.