Default/startup number of panels in config.toml

[Seyloria]

I love double panel file managers like Krusader/DoubleCommander or mc but id like to more or less fully replace them with spf.

A neat little addition and i guess hopefully rather easy to implement addition would be a "startup_panel_no" value.
E.g. you could define a value between 1 and 4 and the number of panels are opened on every spf start.
Default dir could be applied only to panel 1 or all(maybe with an additional value in the config, but not sure if necessary or bloat).

Thx for reading 👍🏻

[yorukot]

#1098