Pin posts to profile page

[ByteOtter]

What does this PR change?

provide a short description what exactly your PR changes here

Tick the applicable box:

• [x] Add new feature

• [x] UI improvement

• [ ] Changed routing

• [ ] Security changes

• [ ] Testsuite
  

• [ ] General Maintenance

UI changes

provide description here or remove all unapplicable lines below

before: Posts could not be pinned to the user's profile page.

after: Posts are now being able to be pinned to a user's profile page. Also, post-preview was split off to be included into its respective html files.

• [x] DONE

Links

Finally fixes #21

• [x] DONE

Documentation

provide description about documentation done here or remove this line

• No documentation needed
  

• [x] DONE