Adding images related to the Play plugin.

Images for the Play plugin for Jenkins.
Replacing link of Vida Suica to Play plugin.
Updating year in academic page.
Adding user manual of Play plugin for Jenkins.
Removing typo in the footer pages.
Adding Jenkins and Play logos.
Replacing icon main page.
Organizing stylesheets and academic page

The navigation bar was remade with a cleaner design.
Several redundancies in the stylesheets were removed.
Play for Jenkins tutorial redesigned