Improve styling in Tocbot block

[olafgrabienski]

(1) Remove text-decoration: Many current browsers style all links by default with text-decoration: underline. With text-decoration of links, the Tocbot block looks quite nervous. In my opinion, the links looks better when not underlined.

(2) Adjust height and position of current item marker: The green markers aren't big enough and look out of alignment.

[olafgrabienski]

Here's a text-decoration comparison:

With text-decoration (underline)

Without text-decoration