Adding option to calculate C4

This adds the option to calculate the ECF ratio C4 since it is needed for the ongoing 4-prong tagger development. The option is turned off by default due to its large computational requirements. Additionally, checks are implemented for the DoC3 and DoN3 flags before assigning a non-default value for those quantities. This will help to prevent unexpected behavior when they are turned off.

Tagging @cdelitzs, @sschramm, @adattagu, @farooque, and @bforland