Cache nutritional values for plan

[rolandgeider]

Found during #241, dummy generator for nutrition plans: if a user has many plans (approx. more than 25), the overview renders slowly and too many DB-queries are fired just to calculate the total calories. Some caching of the values is probably the easiest solution, similar to the canonical_representation for workouts.

Steps:

• cache the nutritional_info dictionary in NutritionPlans
• add signals that delete the cache key everytime a NutritionPlan, Meal and MealItem is added, edited or deleted.

[brotich]

@rolandgeider is this issue still a priority? I would love to take a stab at it based on some of the work done by the folks at @andela

[rolandgeider]

Hi @andela-brotich! yes, while this is not priority 1A, I still want to solve this issue

[brotich]

@rolandgeider cool. Will start on this on the weekend and update ASAP

[rolandgeider]

👍 Great!

[rolandgeider]

Cherry-picked from andela/wg-millennium-falcon#29