Search dialog, implement scrollbar and up/down nav

[SimonN]

Lix 0.9.41.

The search dialog will be more interesting in the future when the multiplayer levels are tagged. Let's look into the missing features in the search dialog:

• Search results cap at how much fits into a single page. The scrollbar is disabled. Let's find more results and make them scrollable.
• When you aren't typing search terms, add up/down keyboard navigation (like in other browsers) for search results.
• Maybe offer popular tags as one-click search queries?

See also: Topic: Search list should show all results on Lemmings Forums.