UI changes (I hope for the better)

- applied last web2py layout and its scaffolding files (including
bootstrap 2.3.2)
- improved the scrolling to the selected paragraph
- now the buttons [buy print] and [pdf] are in the header not in the
sidebar and search form complies with twbs
- implemented a "go back to top" button
- better rendering on ie7
- the html source is more orderly (javascript just before the closing of
body tag and css rules in an external file)
- the .inxx elements have been hidden because they extend the page width
(I understand they are used only for building the printable book index.
Anyway, if this is wrong remove line 13 from web2py-book.css)