Rep4Lev: Implement Up/Down Nav (Keyboard-only Highlighting)

[SimonN]

Lix 0.10.17

In the singleplayer browser, when you select a level, you can choose "Load Replay" by clicking on that button or by hotkey. This opens the find-replay-for-given level dialog, which I call Rep4Lev internally.

In Rep4Lev, you're forced to select the desired replay by clicking on it with the mouse.

Unlike in the singleplayer browser, you cannot use up/down navigation to pick your replay in Rep4Lev. I haven't implemented up/down navigation because highlighting makes no sense -- the first click immediately selects the replay to run it. I've implemented up/down navigation only for highlighting browsers, e.g., the singleplayer browser, where the first click highlights and the second click selects.

Thus: Implement up/down keyboard navigation for Rep4Lev.

@geoo89 has wished for this for years. Aed it feels more like a bug than a mere missing feature.