Include a generic Wallet actor constructor in the actor systems and allow
passing in a generic Wallet actor implementing xtra::Handlers into the cfd
actors.
Rename 'Maker' and 'Taker' to 'MakerActorSystem' and 'TakerActorSystem' for
readability.
Co-authored-by: Mariusz Klochowicz <mariusz@klochowicz.com>
We almost always have the entire `Cfd` available when we call this
function. It is therefore much easier to simply pass the entire
`Cfd` in instead of selective data.