Use buttons for Continuous record start/stop instead of checkbox.
Grey-out Continuous settings checkboxes if we are already doing a Continuous
recording.
Added button to (re)show the Replay dialogue; greyed-out if we are not
replaying.
Various other tweaks.
E.g. for recording a group flight, significantly reduces recording size because
user aircraft signals info is very detailed compared to multiplayer packets.
New dialogue is accesible from the File menu.
Allows enable/disable of three new features: multiplayer record, continuous
record and recovery snapshot. Also moved load/save tape from the file menu into
the new dialogue.
Also removed recently-added flight recorder items from the multiplayer dialogue.
The recovery snapshot interval is 1s second if enabled. Might be better to make
it longer, e.g. 5s, but don't know how to change checkbox value.
