Group the price related contribution items in a sub-menu

[teolemon]

Problem

• In My Contributions, Group the price related item in a Prices sub-menu (gala pointed out that there were too many items)

[teolemon]

• @monsieurtanuki @raphael0202 @raphodn @g123k I created a mockup above.
• Having this section means the News system can potentially link to it instead of an external page.
• This in-app page could have the deeplink prices.openfoodfacts.org, and become the "landing page" of Open Prices within the app.