Include Alternative Fonts: Arimo, Liberation Sans, Nimbus Sans L and Selawik

This is originally suggested as a workaround for Bug #43, where the devs may use either macOS or Windows styles to make some Linux webapps.
To prevent default Linux font to be used, which may cause metric problems in user interface, I would suggest to include some alternative fonts which are most likely to be available in Linux distros (except Arimo and Selawik, which is available in Google Fonts and Microsoft's GitHub repo respectively).