Preview and voting page look alike

Fixes #400.

The preview now looks like the voting page except:
- the text boxes are smaller
- the voting button was replaced with a back button
- the interactive ```I can't give feedback``` button and the respective info box have been removed and the individual contributor boxes can't be collapsed
preview is not set when the page is called as a voting page. then it's not true but also not false.
i could add a new filter for checking that.