#12 : Better route managment

The main purpose of the MR is to solve #12 (closed):

In 0.2.0, every route was added directly in the initialization of the express web server. The dev made for #12 (closed) is to set the router of the site as a middleware of express, a mean to separate the actual express setup from the custom behavior of the server.

Now, the express server take the main router as middleware (with the use function). This main router also integrates as middleware routers, page specific in order to create a hierarchical routing mechanism.

A minor unrelated change also appears in the MR: an unused favicon has been removed.

If the MR is accepted, make sure to close issue #12 (closed). Thanks!