Reduce default heading font sizes

[gosko]

The heading font sizes are quite large on desktop devices – 2.625rem for h1, 2.125rem for h2 and so on. This seems appropriate for the parts of our web site that have marketing or brochure type content, but not for most of the site which is quite text-heavy. The huge headings seem out of place and make the pages difficult to read on pages like the Help or Contact pages, but also on other parts of the site like the TR page, calendar entries or WG summary pages.

I believe most pages on our site should use heading sizes closer to the browser defaults as suggested in the HTML5 spec (2em for h1, 1.5em for h2, ...), with bigger fonts used only in special cases like the home page or ecosystem pages.

I haven't done a close review of the page templates to see which of them should use what size headings, but from a very quick glance maybe the larger headings could be used on the Home page template, Landing page template and Business ecosystem template, with normal size headings used on the rest?

Some related issues: #207, #459, #400