Add missing javadoc

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Make NoHttpBody a singleton.

This would avoid the useless creation of empty objects.

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Add javadoc in the wisdom-maven-plugin

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>