Add option that provides a sh command to format status bar

[EmmChriss]

No description provided.

[gokcehan]

@EmmChriss We can add an option to customize the format of the status line. I think you also want to run arbitrary shell commands within this status line format. Do you have a use case in mind?

[EmmChriss]

I believe there'd be many use cases, but the specific one I'd like to implement is the disk usage of folders with du
It would also be useful to make lf git aware

[EmmChriss]

I believe the more options of customizations are added to a barebones app like lf, the better

[camoz]

I believe the more options of customizations are added to a barebones app like lf, the better

A possible disadvantage is that the additional code has to be maintained. Also, running du for every selected folder seems very inefficient, provided that one usually only sometimes need that information. ranger has a nice feature where when you press dc on a selected folder (which runs get_cumulative_size), the cumulative size of the folder is shown next to the folder name. Such an on demand behavior would be better suited for something like du, IMO.

Also, I'm not sure how this is supposed to work, but isn't the status line updated on every new selection / cursor move? Would that mean that a sh process would be spawned on each cursor move, for updating the status line? That sounds quite inefficient to me.