fix: correct base quantity labels display in meal editing screen

[TomAFrench]

This PR fixes a few issues introduced in #115, notably:

• The space was lost between the macro label and the base quantity, i.e. "kcal per100 g" instead of "kcal per 100 g"
• The default 100g was still included in some internationalisation entries which resulted in "protein per 100 gper100g"

I've updated the .arb files but it's not entirely clear how I should regenerate the localisations.

Running dart run package:intl/generate_localized.dart as suggested in the existing generated files just results in the error Could not find file 'package:intl/generate_localized.dart' Based on flutter_intl in the pubspec.yaml file it looks like you're using this extension for intl but if I regenerate the intl files using that then it results in a few hundred new entries.

Feel free to push the updated intl files onto this branch directly but it would be nice to have a documented process for how to regenerate these.

[TomAFrench]

Looks like @shoutingcatana also brought up the issue of developer documentation on how intl is done. I'd be happy to set up a CI check to ensure that the generated intl files are correctly generated if you can share some pointers on what the process is.