Rethink what is included in the Benchcab class

[ccarouge]

Initially, the Benchcab class was to be used to define the CLI. There are now quite a few additional functions and it starts to feel like it contains what we don't know what to do with. #291 is adding an extra function there.

I am also not keen on the functions that have arguments (self, config) because config is an attribute of self already. And when passed via argument, we pass the value of self._config. So it seems we are mixing 2 different designs/ideas.

@CABLE-LSM/admins what do you think?