o The metaelements and metasources now carry the name, the loader
    resolves source names now.

  o Element/Source factories dont require a name anymore as they
    are already in the meta objects

  o Pipeline no longer composes names

  o Element.name is now the original project relative filename,
    this allows plugins to identify that name in their dependencies,
    allowing one to express configuration which identifies elements
    by the same name that the user used in the dependencies.

  o Removed plugin._get_display_name() in favor of the plugin.name

  o Added Element.normal_name, for the cases where we need to have
    a normalized name for creating directories and log files

  o Updated frontend and test cases and all callers to use the
    new naming

PluginContext, ElementFactory and SourceFactory reside in
entirely private modules, as such they do not need a leading
underscore to indicate that they are private.

This makes the code nicer to read without causing private
things to be considered public.

Now modules import as:

  from . import _site

And refer to things as _site.root, _site.default_config etc.

Also now follow principal of least underscores

This file is for site installation relative path names
for convenience, it's not where configuration stuff is stored and
it's an entirely private detail.

Better to have a separate file for each class clearly addressing
it's purpose with it's filename.

  Source base data model -> source.py
  SourceFactory -> _sourcefactory.py
  Element base data model -> element.py
  ElementFactory -> _elementfactory.py

Also moved the _plugin.py to _plugincontext.py, since the object
is infact _PluginContext, lets follow this rule all around for
code clarity.