smif app fails to render some pages some of the time

[tomalrussell]

With nismod/nismod2 config, flushes out some fragile assumptions:

• sos_model scenarios should be lists (not objects)
• scenario description should be empty string - this might be coming back as a list

Probabe fixes for these with:
a) stronger guarantees that the API returns well-formed data structures
b) stronger error boundaries on the client (at least avoid total white-screen failure)