Moves the modules in lib/ to app/models and lib/integrations to app/integrations.

We decide on app/lib v. lib/ once and for all

It is also worth noting that lib/tasks typically has application-specific tasks, thus not fitting into the condition for lib. Which makes me question the criteria for lib

Going by the intended purpose of lib/ ("pending extraction"), I think lib/assets should remain (as those are assets pending extraction).

lib/ is intended to be for non-app specific library code that just happens to live in the app for now (usually pending extraction into open source or whatever).