[Improvement] Easier override registration and emulated program functions discovery

[maximilien-noal]

1. Override registration and assembly loading is a bit overly complicated.
   The IOverrideSupplier and related code could be simplified.

2. The emulated programs functions Dictionnary that is passed around could be a higher level API, and inversion of dependencies could be applied.

3. The emulator could be more open about its inner workings, so users could plug in their code more easily