[KEY FEATURE] Build model directly in UI

[brynpickering]

This doesn't depend on any fancy visualisations, just a dependency tree to define connections between model components (the network), and tables in which parameter values can be defined (the base scenario).

[clizbe]

Good one. I think I wrapped it in #26 in my head, but they're indeed different.

Related:

• [KEY FEATURE] Handle multiple scenarios #26