Sets the application name (the *webapp-name* variable). 'name'
must be a symbol. This symbol will later be used to find a
package that defined 'init-user-session' - a function responsible
for the web application setup.

Additionally, 'name' will be used by 'page-title' to generate the
title of each page.

'init-user-session' must be defined by weblocks client in the
same package as 'name'. This function will accept a single
parameter - a composite widget at the root of the
application. 'init-user-session' is responsible for adding
initial widgets to this composite.

'description' is a short description of the web application (ex: “A
technology demonstration”). *webapp-description* will be set to this
description (unless description is nil), and the value will later be
used by 'page-title' to generate the page titles.

By default 'defwebapp' adds the following resources to
*application-public-dependencies*:

Stylesheets: layout.css, main.css
Scripts: prototype.js, weblocks.js, scriptaculous.js