Create about page

[niccokunzmann]

There should be an about page for the app inside of the app.

• [x] add about page
• [x] reach the about page in some way from the main page
• [x] link to the project issue tracker
• [x] link to the project github
• [x] link to the project website
• [ ] show build version and link that to the commit on github
• [ ] link translation page
• [ ] add trademark information