Missing client roots definition API

[ptitjes]

Describe the bug
It looks to me that the Client class is missing the API to define roots.

I would be happy to provide a PR.

To Reproduce
N/A

Expected behavior
I believe Client should have an init { } block registering a handler with setRequestHandler for the root list method, have some roots variable containing the defined roots and corresponding API to add/remove roots.

Logs
N/A

Additional context
N/A