You need a fully functional TTRSS server
Install this content into your_roundcube_root/plugins/ttrss/
Configure your config.inc.php to add this plugin
Go to your settings into your RoundCube instance and add your login and server

Search menu
Not refresh headlines on update a label on articles
Find a way to count all articles by feed (and activate button last page)
Maybe adapt the code for older skins, if there is interest from people (not plannified yet)
Optimization

Due to API limitation, you : 
> Cannot create, rename or delete label
> Cannot create, rename or delete category
> Cannot move Feed to another category
> Cannot change order id of the feed (for this reason, I choose to sort by alphabetic order)

So for all these actions, you need to log in into your TTRSS instance, and while the API doesn't change, I cannot change that

Because I use localStorage for storing current feeds selection and more, the use of multiple instance of roundcude_ttrss on same browser can be hazardous
But it takes the advantage to let you your session when the browser is closed at the same place than before