Make sure special chars don't overlap with the right-hand-side labels
Improve comment textarea rendering

This includes:
- moving from buggy no longer maintained patched version of jquery.textarea-expander.js
  to a more modern and polished jquery.autosize.js
- rearranging layout for extras-bar to make it more compact and detached from the
  comment form itself
- make comment form appear on one line with the button and resize properly
- when comment form is expanded, focus on it to avoid extra click
- make last comment more prominent on screen (it shouldn't look like
  suggestions or similar translations)