Added kilojoules property to ingredient model (Issue #568)

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Proposed Changes

• added "energy_kilojoule" property to Ingredient class in wger/nutrition/models.py

• added kilojoules to display on ingredient details page in wger/nutrition/templates/ingredient/view.html

• added to wger/nutrition/static/js/nutrition.js, making kilojoules responsive to updates in ingredient amount according to user input

• added test to wger/nutrition/tests/test_ingredient.py, verifying correct kilojoule conversion

Please check that the PR fulfills these requirements

• [✓] Tests for the changes have been added (for bug fixes / features)
• [✓] New python code has been linted with with flake8 (flake8 --config .github/linters/.flake8)
  and isort (isort)
• [✓] Added yourself to AUTHORS.rst

Other questions

• Does this PR introduce a breaking change such as a database migration? (i.e.
  what changes might users need to make in their running application due to
  this PR?)

No

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I worked on these changes with my partner, @derekli17, which is why his name is also included in AUTHORS.rst. We are currently undergraduates studying computer science, so if you have any feedback or want us to make changes, please feel free to let us know! Thanks.

[rolandgeider]

While showing everywhere both the kcal and the kJ would break the UI flow, I'd add them to the nutrition list and the nutritional data table under the plan, then this would be ready to merge

[nopinter]

Hi, thanks for your feedback! We've implemented your suggested changes. We found the "4,184" / "4.184" issue very funny, but that now is fixed 👍 . Additionally, we wanted your feedback on an aesthetic issue, which we've attached a picture of.

As you can see in the red circle, sometimes the kilojoules wrap around onto the next line. Let us know your thoughts on this. We'd be more than willing to change some of the HTML/CSS to make it look cleaner if necessary.

[rolandgeider]

I also had to laugh when I opened a plan and saw like half a million kJ 😂

And as for the line wrapping issue, we can save some space by removing the decimal place but other than that I wouldn't change much

Edit: it has technically nothing to do with this issue, but can you perhaps take a look at #581?

[nopinter]

We have experimented with removing the decimal place, but we are still observing the line wrapping issue. We didn't make any further changes for this reason

[nopinter]

Also, we would be willing to take #581 instead of #575 ! I'll will comment on those to reflect this

[rolandgeider]

Merged, thanks!!