Completed and remaining todos are shown and hidden with CSS. 

Reverting fix from 69e5778 that is now not needed anymore since task deletion works as it used to.

Completely different approach to fixing this problem. One might also completely get rid of the tab and simply change a css class to define if the remaining or the completed todos are shown. Then one wouldn't need to render the list twice.

I tried to ran the casper tests, but somehow they don't want to work yet. So make sure to run them on your end before merging this.

Refs #226, #73