Loading replays progress bar

[Asuna Yuuki Nagato]

Steps to recreate:

1. Replay->Load Replay
2. Click 'OK' in Replay msgbox
3. Select a .zplay file and click 'OK' in the Load Replay (.zplay) window
4. Player window freezes for several seconds

There should be some kind of feedback that the player is trying to load the replay and it hasn't just frozen.

[Asuna Yuuki Nagato]

This loop in load_replay is what is taking so long:

    while (util::portable_get_line(file, line))