Tag view and tag lookup page

Or at least the very start of them. The idea behind the framework should
be getting clear now. There are some TODOs left, but due to the lack of
internet connection right now I can't fix these.
The tag page is starting to take shape
First draft of navigation on tag's page
Copied the about page to the new website
Added title of the About page
Started converting the chapter and browse overview
Fixed styling of the browse page
Fixed a warning in php/pages/index.php
First draft of navigation on the chapter lookup
Some improvements to the browse page
Default font Arial

This makes Firefox display things more like Google Chrome. But some
other fonts could be tested too.
More working links in the navigation