ui: display a proper file tree for playbook files (or port file tree view from 0.x with bootstrap-treeview)

[dmsimard]

What is the idea ?

ara 0.x has a neat tree view of playbook files with a certain amount of interactivity:

The implementation is likely still compatible but would require an additional dependency on bootstrap-treeview and pyfakefs: fb09b65

I don't think we can get away without bootstrap-treeview. There is probably another way without pyfakefs but it's what I had come up with at the time that worked :)

[kfiresmith]

As a user: This looks fantastic! Would find this useful in 1x