move responsibilities DbObjectExecutionFixture => ExecuteProcedure

all the functionality dealing with exceptions has nothing to do
with the Insert fixture, so can be safely moved to the ExecuteProcedure
class
refactor ExecuteProcedure, DbObjectExecutionFixture

split execution into clear parts:

* set parameters/columns
* execute
* validate outputs
DbObjectExecutionFixture: extract #executeStatementExpectingException
better factoring of ExecuteProcedure and StatementExecution

* extract Savepoint in StatementExecution
* StatementExecution manages saving and restoring of savepoints
* ExecuteProcedure can query StatementExecution for received exception