Fix consistent behavior with multiple Go statements

[carl-berg]

Relates to
#19
#17

Currently DataDude will clear instructions between go statements
But the rest of the context is retained meaning previously inserted rows are kept but the go execution will run everything again and also inspect dependencies and generate auto-fk's (if configured) again, even if they have been previously inserted which may not be what you want.

Some ideas:

• We could use a setting to instruct DD how to behave if a second go is stated
• Another idea could be to always clear previous state when using Go, but add a Continue method that tries to utilize previous information. Possibly Go method could return an object that has a Continue method...