Feature request: Stop using hardcoded plural forms

[turtlegarden]

• [x] My proposal does not exist in the PLANNED & NOT PLANNED.md document
• [x] I have not found any other opened issues on the same feature request
• [x] I believe this fits within Warehouse's scope of Flatpak management

Describe the feature idea in detail

The app currently uses hardcoded singular and plural forms. This is not how all languages work: in stead, the app should use the ngettext function to get the correct form for the number that will be put into the template. This change does not require much work, and although it will void some translations, it will be worth it, especially for all languages which have more or less than 2 singular/plural forms. (And the translations were already basically voided by the last update anyway :P)

[turtlegarden]

This would, however, require going through all strings in the project and see if there are any hardcoded plurals at all. That may take some time!