This is the minimal import that should seemingly work, although it would need to be honed
based on the actual data filled one.

Some questions outstanding (unsure whether to resolve now or later)

1) do we want any defaults for utm_medium / utm_source / utm_campaign?
    These can be added to the csv by the importer but Stripe, for example, used MGEventEmail

2) Currencies - the data sample shows us receiving in EUR & getting settlement in Euro. I changed the line I am checking to settlement in USD - can we expect this to be the case? Otherwise I guess ... complexity.

3) Fees - the data sample has some rows showing fees. I have assumed we will simply no import these as
I didn't spot a precedent for this

4) Refunds - the data sample has some rows showing refunds. We don't have a prededent for this -
do we need to handle it

5) Deduping - after discussing with Elliot I have not done any dedupe handling (although I guess the deduper will dedupe some after import) Elliott suggested the data quality might be pretty poor in terms of names etc anyway.

6) Sample data "Satoshi Nakamoto" - that one was in there when I got the sample - nice touch.

Bug: T192953
Change-Id: I21122cf7444caefb0fd21625169cdf8236562f72