Implement printer-friendly view

[pkwagner]

Fairly simple css change causing the browser to only print out the right pane (a preview is available when hitting Ctrl+P and also allows a clean PDF export). The feature could be refined by adding a title and removing the iCal link. However, this would probably require some HTML changes and I didn't have a look into the templating mechanism yet. The resulting sheet looks the following:

I know it's archaic, but I really like having a physical print of my schedule 😄

[drcicero]

A useful feature in just six lines, nice :+1: