Add concept of servings when entering meals

[noizwaves]

For food, it makes sense to enter their consumption as non gram or millilitre amounts. Take for example 1 banana or a cup of baby spinach.

Allow foods to be annotated with servings information, ie. 1 'servings' equates to Y g or ml. Ie. 1 'piece' of banana equates to 75 grams.