GitLab

- Remove duplications and don't require a specific file for every
subtype
- Add specific Twitter metadata since this is probably what is used most
for our users
- Use PNG logo since SVG is e.g. not supported by Twitter
- Add specific excerpts where not available yet

- Move style guides to the bottom into one section
- Move workflow section to the top

Blog post:
* changed publication date
* added section which explains Review Apps
* added screenshot
* rephrased text duplications
* fixed typos
* referenced contribution guide

Contribution guide:
* added section which explains Review Apps
* rephrased text duplications
* fixed typos
* referenced blog post

A discourse has been added regarding the necessity of alternatives for hover interaction on mobile devices and possible approaches to solve such issues.