Too many hard-coded parts

## Prerequisites
- [ x] I have searched open and closed issues for duplicates.

## Describe the bug
The theme's files contain many hard-coded parts, like links and messages, making reference to elementary OS's blog, which makes difficult for other people to use it in their own blogs.

### Expected behavior
The theme should make use of variables that can be configured via the `_config.yml` or the front matters, rather than editing the theme's files directly.

### Describe the solution you'd like
I really like this theme and I'd be happy to contribute to it by submitting a PR replacing the hard-coded parts with variables, if you're okay with it.

## Platform Information

- [ x] I'm using the latest version from git that I've manually compiled
- [x ] I'm using the latest released stable version

I'm using this theme on my self-hosted blog running on an Nginx + Ubuntu 20.04 server.

Inspect the theme files for hard-coded links and messages, then compare them with the available _config.yml and front matter settings. Done means the identified elementary OS references can be configured by users without editing the theme files; no tests or specific entry points are mentioned.

Written by the indexing model from the issue text.