find-sidebar: only update when search job finishes

Currently, the search sidebar is updated whenever the search job yields search results for another page. This, however, comes at a cost. As such, it makes sense to wait for the job to finish before displaying results.

Additionally, the window plays a heavy role in controlling the sidebar by passing through signals. Instead, it should only listen to those signals that are relevant to the window itself.

The UI should better reflect the search progress, especially with this change.

Fixes #75 (closed)