timeline: add nip50 search timelines

Fixes: https://github.com/damus-io/notedeck/issues/456
Signed-off-by: William Casarin <jb55@jb55.com>

crates/notedeck_columns/src/lib.rs

@@ -27,6 +27,7 @@ mod profile;
 mod profile_state;
 pub mod relay_pool_manager;
 mod route;
+mod search;
 mod subscriptions;
 mod support;
 mod test_data;