[STYLE] Nav tabs - let <a> occupy entire tab
[STYLE] Nav tabs - let <a> occupy entire tab

By setting it to `display: block`, and putting the left and right
padding in it instead of in the parent <dd>.

Signed-off-by: Pang Yan Han <22594c345857f664c61cd411f607c4d40a9d4af9@gmail.com>

yanhan/cljs-nusmods,yanhan/cljs-nusmods,yanhan/cljs-nusmods