Purchase event messages might sometimes be unclear

[Esinko]

Purchase events show up as positive changes against the current account total, while returning a can (for example) show as negative changes to the account total.

I think some general cleanup for logging purchase events should be done too.

I think it would make more sense for buying a coffee to log:
Bought 1x Coffee 0.19e
Instead of:
Bought 1x Coffee 0.19e (Total 0.19e)

And when returning a can to log:
Returned 1x Can return 0.15e
Instead of:
Bought 1x Can return -0.15e (Total -0.15e)

Perhaps even more specific messages should be made?