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
ExecuteProcedure: bugfixes, better factoring
restructure ExecuteProcedure with specific expectation classes
break DbObjectExecutionFixture into classes
DbObjectExecutionFixture no longer uses fit Bindings
extract cell processing into own class
rename CellTest => CellAction
CellAction: remove unused method
modularise CellAction
made cell handling more generic
don't fetch actual values twice
extract actions into own package
a bit more cleanup
extract the concept of Row into own class
move classes to more appropriate packages
split out fit-specific parts of Cell into FitCell
moving classes around