Metadata JSON loading and refresh() fix

*mm_util.py*
create get_default_metadata_data() and get_child_metadata_data() to load metadata JSON centrally, replace references in the project to the file name with this function.

*mm_project.py*
Fix for https://github.com/joeferraro/MavensMate/issues/6

Checks for project root or /src directory to refresh all metadata, if not checks that metadata type could be found before adding it to the refresh list.

Update hard reference to metadata json with mm_util.get_default_metadata_data()