fixed preview display for nodes without files
added functions
Merge pull request #11 from paczian/master

fixed preview display for nodes without files
removed submodule
readded submodule
update Retina
updated Retina
updated Retina
updated Retina
removed widget variable from global scope
updated readme
updated retina
changed load_data to import_data
Merge pull request #12 from paczian/master

updated Retina
merge conflict