CSS code was divided in multiple files, however this was not practical
for organization since different pages needed different CSS classes one
another, that were in most of those CSS files.
This commit brings (mostly) everything in one file with a table of
contents on top.
An exception is made for fonts, that are now in a separate "fonts.css"
file, since they contain fundamentally different things.
Classes organization is not yet complete, however a great part was done.
Next commits will finalize this organization and finish moving classes.
Signed-off-by: Lorenzo Dellacà <lorenzo.dellaca@mind-overflow.net>