:lipstick: Breaking up implementation of lookup

Using separate macros to find and to do actual lookup. Simplifies the layout of the main macro a
bit.
Adding hook for look up packages

Hooks should consist of scripts in a given directory (per hook) with a given filename (per package).
A function exists to write these hooks as cmake scripts. Only one hook is currently called:
POST_LOOKUP. It is executed if the recipe has already been included once.
Add ability to install python stuff more easily