In order to prevent the global ./style/default.css from growing until
it's a complete mess, it is also possible to modularize css stylesheets
and javascript files.

If a module contains a file called style.css, it is automatically included
in the generated HTML page of the module, or any module that declared this
module as a dependency.
The same goes for a file called clientscript.js. Any module containing such
a file will have this script included in the generated HTML.

This way you can have module specific CSS definitions. Some of the
definitions in ./style/default.css should be moved into modules over
time (TODO :)), since they are only used in one module.

Thanks to the dependency mechanism it is possible to have dedicated css/js
modules, like "js_chart" or "js_circles". An example is the module
"statistics", which defines js_chart as a dependency in its config.json.
The result is that js_chart/clientscript.js is automatically included
in the HTML output of the statistics module.