Add information needed for restart capability into TaskConfiguration

[WardLT]

Is your feature request related to a problem? Please describe.
Sort of. I've added in the capability to specify the directory in which we perform an NWChem calculation so that it can restart computations where QCEngine was killed before NWChem finished (#330).

For now, I store that option and another that controls whether we event want restarts in AtomicInput.extras

If we want this capability to be used across more codes, we should add "where to store restart files" and "do I allow restart" options to TaskConfig. That way, they go along with all other options that control how a task is executed (e.g., the number of cores).

Describe the solution you'd like
Adding more options to TaskConfig

Describe alternatives you've considered

• Storing the options in each code's specification file, which will lead to standardization problems.
• Storing the configuration in AtomicInput, which means they will be separate from all other execution-related settings (e.g., where to place all scratch directories).

Additional context