Cleanup QTableView autotest:
 - use range-based for loops where possible
 - use nullptr
 - use member initialization
 - use new signal/slot syntax
 - remove a lot of c-style casts
 - use static invocations
 - use override
 - instantiate objects on stack instead heap to avoid memleaks

Change-Id: I52fee26697b1732afa9f965e600d4c59551370ce
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>