Add a minimal implementation of Harvard meal guidelines

[Gallaecio]

Please, ignore this PR until it is no longer a draft. I have zero experience with this tech stack, so it is going to take me a while to figure things out.

To do:

• [ ] Rename “Macros distribution” to “Meal guidelines”.
  • [x] Do it wrong.
  • [ ] Figure how internationalization works and/or how to trigger an update of the generated folder, and make the change properly, also renaming the message ID accordingly.
• [ ] Implement a “Harvard (experimental)” entry under “Meal guidelines”.
• [ ] Harvard: remove the carbohydrate requirement, to be replaced with other requirements later.
• [ ] Harvard: replace fats with poly fats, and require 0.08 of energy.
• [ ] Harvard: calculate min protein as max(0.1 of energy, 0.8 g * weight in kg).
• [ ] Harvard: add a 25 g of fiber requirement.