Use review apps from gitlab to provide demo

Description

Use review apps feature of gitlab to show changes made in merge requests (on branches) and on master branch.

Explanation

Useful to demonstrate features before merging their changes without a need for anyone to install and start the environment locally (on his/her computer).

Mockups/Screenshots

(If possible, provide mockups or screenshots, which demonstrate the feature)

Dependencies, issues to be resolved beforehand

It would be useful fake response of items from the backend using #37 (closed)

cc: @sebastianlange @krlwlfrt