[Frontend] Add Impressum / About to UI

[fionatiefenbacher]

User story:

As a user I would like to see what the website is about, who I can contact and who worked on it. The impressum is important for legal reasons.

Acceptance criteria:

• [x] Footer with information what the website in short is about
• [x] Impressum with all information in new window

Considerations:

• Impressum in form of a pop-up window similar to https://ilimodels.ch/
• Short Info in the footer about the project, which may also be linked to the pop-up impressum