Improve ComputationalResourcesWidget

[superstar54]

Currently, the ComputationalResourcesWidget is used to select the code with a default_calc_job_plugin. But not include number of nodes, number of cpus etc.

So either we add support for setting up the computer resource (nodes, cpus), or we change its name similar to AiiDACodeWidget.

Besides, there are some settings that are special to a code, for example, the parallelization levels (pools, images, nk, etc.) in the pw.x code. It would be better to expose some entry point that one can customize it.

[superstar54]

Here is a use case, aiidalab/aiidalab-qe#566. I created a new ComputationalResourcesWidget from one of the aiidalab-widigets-base.