removeEmptyFolders()
    {
        // Set up
        let removedCount = 0

        // Recursive remove
        const canRemoveFolder = function(folder)
        {
            // Each folder inside current folder
            for(const _folderKey in folder.folders)
            {
                // Try to remove folder
                const _folder = folder.folders[_folderKey]
                const canRemove = canRemoveFolder(_folder)

                // Remove folder
                if(canRemove)
                {
                    removedCount++

                    // Delete
                    folder.folders.splice(_folderKey, 1)

                    // Callback
                    if(typeof _folder.onRemove === 'function')
                    {
                        _folder.onRemove.apply(this, [_folder])
                    }
                }
            }

            // Can be removed
            const folderKeys = Object.keys(folder.folders)
            const filesKeys = Object.keys(folder.files)

            if(folderKeys.length === 0 && filesKeys.length === 0)
            {
                return true
            }
            else
            {
                return false
            }
        }

        // Try from ./
        canRemoveFolder(this.folders[0])

        // Update counts
        this.updateCounts()

        return removedCount
    }
Browse every folders and remove empty ones
@return {Number} Number of removed folders