Refactored ConnectionResolver to load the right database connection
class instead of only setting the right grammar. Using FuelPHP with
Postgres showed that processInsertGetId was called using the default
Processor instead of PostgresProcessor which passes an incorrect 
$sequence for Pdo::lastInsertId.
Merge pull request #368 from CodeYellowBV/master

Refactored ConnectionResolver to load the right database connection