Copy over prelim section.

Mostly from Kyle's dissertation with homology from the SoCG 2009 paper.

Minimal changes made to allow compilation and avoid adding new full
sections.
Remove unneeded note.
Fix face-edge notation.
Clean up prelims section and add main lemma.
Cuts are edge-sets.
Keep weight vs. capacity consisent.

And leave a note on their usage.
Add a conclusions section.