Value added and bug fix.

- Edit file with no name will remain with the old name
- Auto rename when the filename is already exist
- If user leave blank in name field, default folder name (RBFolder) will be used
- Auto rename when the folder name in the same folder has already existed
- Auto rename slug when the slug has already existed
- Edit folder with no name will remain with the old name
- Physical files are not deleted when folder is deleted