Fixed font size mentioned in #165

Adjusted font sizes of headings h1-h4 in div.entry-section to the proportion of the parent headings (h3 with font-size: 24.5px) and the normal text (font-size: 13px).

The result is a more balanced layout concerning headings in blog posts. See here: https://internal.innoq.com/blogging/blogs/77/entries/

**NOTE:** The effect on weekly-statuses seems ok to me: https://internal.innoq.com/blogging/weekly_statuses/219
Merge pull request #169 from aheusingfeld/master

Fixed font size mentioned in #165
I typically don’t merge here, but this seems a pretty safe change.