Add support for the upcoming merge mining chains
**Feature request**
Darkfi, Tari, and TownForge are planned to be merge mined with Monero.  Add mining these coins alongside XMR inside Gupax.

**Additional context**
[P2Pool v4](https://github.com/SChernykh/p2pool/releases/tag/v4.0) has added merge mining feature.  This new p2pool feature should become available inside Gupax, when the merge mined chains (DarkFi, Tari, TownForge) complete their implementations.