#12 Allow stored procedure calls as statements in transactions

[MatthiasNicola]

To make the workload driver a more flexible tool and to allow the design of more sophisticated workloads, it would be good if transaction templates can contain stored procedure calls, such as:

call insertDocument(?)
or
call readOrder(?,?)

Things to consider:
- SPs that return no data vs those that do
- What to do with output parameters

[MatthiasNicola]

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Let's test and review carefully before uploading the code changes.