feat(doom): Add vertical center

[polirritmico]

• Vertically center the Doom dashboard.
• Doom code refactor.
• Add the config.vertical_center option (defaults to false).
• Same average load time on my system.
• Fix #354.

Is working for me without any problem in a lot of config scenarios, but I think it needs more testing.

Since this use the same load_packages code from hyper, but with a return, maybe we could move that into utils or something like theme/packages?

Regards