Cleaned up resistor networks script

Created by: fauxpark

After https://github.com/KiCad/kicad-symbols/pull/833, I decided to take a look at the resistor networks script. It now generates valid symbols as of the v5 libs (mainly old footprint/filter assignments and symbol names), but apart from the regular R_Network symbols, they are not quite identical to the ones currently in Device.lib. Seems to be mostly rounding or off-by-one issues, and even-numbered R_Pack symbols are centered on different resistors.

The individual drawing elements are annotated with comments now, so you can more easily tell what line produces what part of the symbol. Hopefully this makes it much less of a pain for someone else with more math skillz than myself to jump in and fix things.