Various UI tweaks to the TOC in Special:Configure

- merge and simplify two identical CSS selectors
- add a little right-padding to TOC so it isn't glued to the content
- add tooltip to the TOC's show/hide arrows
- make a.selected CSS rule apply to sub-items as well
- pull show-hide controls to the left so the entries are aligned
- use minus sign rather than hyphen for alignment and semantic correctness purposes
- place the TOC show/hide arrows so that they don't jump around when clicked on

Change-Id: I745beef8802ae15f6df1c7bd4629556b7ffcaba1