Add attributes and special flags

[sazanof]

Hello!

I use your code in conjunction with Symfony back and Vue front. I needed to get more attributes in order to change the context menu, visual design (for example icons) depending on the type of folder (trash, sent, spam). Therefore, I have made some edits to your code and now there are great opportunities in determining the type of folders that have special flags (\trash,\sent,\drafts.....)

Unfortunately, there were issues with the formatting of the code (reformating in phpshtorm) and there are a lot of changes in the PR (indents, quotes). Maybe we can implement a single formatting for this.

As for my PR, I would be grateful for its consideration and discussion.