Refactor templates to reduce duplication and assist with Translations

[tunetheweb]

It's been noted a few times (e.g. here, here and here) that there is a lot of duplication of code, especially with the translations and it would be good to refactor these to reduce that and keep the code more maintainable in future.

We should probably have a templates/base/2019/ folder or the like and each translation (including English) can inherit from that and only have the translatable text in each language specific directory rather than the current mix of HTML, JS and Text.