Add custom title / translation of categories (#755)
### Prerequisites
Put an `x` into the box(es) that apply:
- [X] This pull request fixes a bug.
- [X] This pull request adds a feature.
- [ ] This pull request introduces breaking change.
### Description
This PR is similar to #754, but updates the categories to utilize Hugos
taxonomy system, instead of the tags .
This PR edits the posts/single layout to use `.GetTerms "categories"` to
fetch a richer model of the categories, and the taxonomy/categories
partial to use this model, instead of just urlizing the category name,
so categories with a custom title, renders correctly on a post.
This also enables translation of the categories shown on a post, while
enabling switching languages on the category page without losing
context.
To show this in action, I've added a translation of the "themes" and
"syntax" categories in the exampleSite into PT-BR, as "temas" and
"sintaxe", respectively, and switched the pt-br page to use the english
category ids so they are seen as the same category regardless of
translation.
Also, this enables customizing/translating the category url, by
specifying a slug and/or url in the category frontmatter.
If you switch languages here on the category page, you'll see the
translated category and corresponding posts, instead of dropping out to
the front page like before.
### Issues Resolved
If you wanted to use Hugo taxonomy system for the page categories, only
the category id showed up on the post itself. This PR fixes that.
### Checklist
Put an `x` into the box(es) that apply:
#### General
- [X] Describe what changes are being made
- [X] Explain why and how the changes were necessary and implemented
respectively
- [ ] Reference issue with `#<ISSUE_NO>` if applicable
#### Resources
- [ ] If you have changed any SCSS code, run `make release` to
regenerate all CSS files
#### Contributors
- [ ] Add yourself to `CONTRIBUTORS.md` if you aren't on it already
Co-authored-by: Luiz F. A. de Prá <luizdepra@users.noreply.github.com>
Martin Hellspong