Add About Page
Created by: LNJ2
Just a simple page displaying the kaidan icon, the version (kaidan, qt, swiften), build date (needs CMake change), authors (developers: marzanna, jbb, lnj; previous developers: geobra; translations: lnj, Ilya Bizyaev - I think thats it) and the copyright (maybe on an extra page).
EDIT: Should be linked in the drawer of #35.