Poll.module cleanup:

* Code cleaning: simpler structures, removed some old leftovers, ...
* Clean URLs everywhere (the old mechanism was broken anyway). Had to get rid of 'inline voting' (i.e. voting with the sideblock and ending up on the same page), but that was a bit confusing anyway.
* Simplified submission form with form_group and streamlined choice mechanism.
* Improved bar rendering in pollresults for themes with avatars, like xtemplate.