[web] Introduce thread ancestors in top bar

Summary:
Introduce thread ancestors list in top thread bar and keyserver owner. I tried to exactly match Figma design.
Right now, it doesn't show names of threads between source and current thread, but it can be easily introduced if there is a need.

Test Plan: Tested the component on threads with different count of ancestors to confirm it is displayed correctly.

Reviewers: palys-swm, benschac, atul, ashoat

Reviewed By: palys-swm, benschac, ashoat

Subscribers: ashoat, Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3148