[Docet-Maven-Plugin] New mojo to create a ready-to-use WAR

[mcRoot]

The idea is to have a mojo which creates a ready-to-use WAR file which contains the built documentation package together with:

• DOCET RUNTIME (same version of the plugin)
• A simple servlet which runs Docet
• A default HTML container page (which a default template or the ability to use an user-supplied HTML file)

we can also add an option to create an "executable-war", that is a JAR file which runs Tomcat or Jetty and deploys the WAR file.
this will be useful too, in order to "view" the documentation without the need to install a Java Web container