Ensure <h5> and <h6> have different computed font size

Ensure <h5> and <h6> have different computed font size

Browsers tend to have a default font size of 16px and the Vector and Monobook
skins use various techniques to end up at 12.8px resp. 12.7px for the bodytext.

Now, in commonElements.css, we have 105% for <h5> and 100% for <h6>. This gives
rounded values of 13px for <h5> and <h6> in Vector and Monobook, making them
hard to distinguish.

This patch enlarges <h5> to 108% in Vector and Monobook.

Bug: 48671
Change-Id: I9d0fccc687ceba05a6af847efc374fdef04f9b38