start replacing the Orocos namespace by OroGen
doc fix
introduction of a separate loading infrastructure, as well as Spec::Typekit and Spec::Project

This moves the loading code outside the Project class, which will
in the end allow to cleanup Project quite significantly in a very
incremental way. The loading mechanisms now create Spec::Project
and Spec::Typekit objects, that are not polluted with knowledge
about the code generation engine.
implement recursive loading of dependencies
loaders: documentation
test: create a clean OroGen::SelfTest module
loaders: separate the loading of textual model representation from the creation of model objects