rose.config_tree: improve pep8 and pylint scores
rose.config_tree: store file lists

If a relative path can be found in 2 or more locations in the linearised
inheritance, it will store the configuration locations in a new list.
Use rose.config_tree to load metadata

Part 1.
rose.macros.trigger: use rose.config_tree

to load metadata.
revert style changes
 #137: add rose edit, rose macro functionality
#137: implement for metadata-graph
#137: document
#137: add override example and test
#137: add rose user guide import mention
Merge pull request #1415 from benfitzpatrick/metadata.config_tree

#137: rose metadata inheritance