prepare executor for bulk insert support
copy from phase #2, send commands separately

Still no functional nor real performance changes, just
breaking this up so I can better test where something
went wrong (if it went wrong)
refactor table transfer, prepare for bulk

The bulk code does nothing yet (and would malfunction
if an executor with the capability set would be used,
luckily such an executor doesn't exist yet, that would
be the next commit).
adjust bulk interface
copying works!