base_nonav_fixed.html: fix content/title blocks for better inheritance
base_nonav_fixed.html: fix content/title blocks for better inheritance

Now all descendants will be able to use `content` block for main page
content (some had previously to use `content-fluid`).

pbanaszkiewicz/amy,vahtras/amy,pbanaszkiewicz/amy,vahtras/amy,swcarpentry/amy,swcarpentry/amy,swcarpentry/amy,pbanaszkiewicz/amy,vahtras/amy