[User story] Category filter

[alexkisielewicz]

As a user, I can select a category from the menu, so that I can find all the posts from the category that I am interested in.

Acceptance criteria:

• A button with a category dropdown menu is provided on the posts page.
• Selecting specific category filters posts on the posts page.
• The user can remove the category filter by selecting the "display all" option.
• Currently displayed category name is present in the UI.