Refactor LPU code

[TK-21st]

LPU.py used to be a mega-file that does all of the following in a single file:

1. Parse networkx graphs
2. Update connections, adding synapses as per needed
3. Update components by adding delay and other memory management variables
4. Setup variable memory
5. pre_run, run_step, post_run

There is a need to cleanup the file for future development and potentially removing some extraneous functions.

This is tracked in feature/refactor branch starting at commit 3e77638