MULE-7433: Add DB connector to mule code base

    _ Removing DbConnection#getDelegate
    _ Improving logging in StatementResultIterator
    _ Renaming parameter in UnresolvableDbConfigException constructor
    _ Adding logging to TransactionDbConnectionFactory
    _ Adding logging to TransactionDbConnectionFactory
MULE-7433: Add DB connector to mule code base

 _ Reverting some added logging from TransactionDbConnectionFactory
MULE-7433: Add DB connector to mule code base

 _ Cleaning TODOs
 _ Created jiras: MULE-7451, MULE-7452, MULE-7453, MULE-7454
Merge pull request #501 from mulesoft/MULE-7433

MULE-7433: Add DB connector to mule code base