Why are Sell actions stored as Buy?

[Mark Jones]

Hi KMyMoney devs,

I've been studying the code base to gain a better understanding of the
KMyMoney model so I can contribute a fix for bug #378377 (Allow investment
accounts to include cash). I keep coming across code that flips a Sell
action into a Buy action on storage (and vice versa on loading) and I don't
understand why this code is required.

I added back the SellShares and RemoveShares actions in my local repository
(for file storage only) and all appears normal. So what else did I break? :)

Thanks
Mark