ISIS-284: moved isis-maven-plugin into core; deleted unused code; todoapp example now references the plugin in its webapp project.
ISIS-284: moving isis-maven-plugin from todo app's webapp module and instead in the dom module.  Supported this by extending the ServicesInstaller API, adding setIgnoreFailures.

Also added into simpleapp example.
ISIS-928: recreating simpleapp archetype
ISIS-928: recreating todoapp archetype