[Enhancement] Add a way to search and find a feed by its name

[Massedil]

With a lot of feeds, it is hard to locate one feed in the list.

Expected: A search text zone to filter feeds (and categories ?) in the main screen.

Context: I now have 550 feeds, 80 000 articles, 800 MiB SQLite database and 14 000 unread articles in my FreshRSS app.