Consolidate charge-threshold cutting methods

[jwaiton]

As discussed here in #912, there currently exist multiple differing methods for cutting charge from hits.

These should be consolidated in a manner that keeps the differing methods, while providing some connection between them.

Two examples off the top of my head would be:

• including each charge-cutting function one after another in hit_functions.py
• providing each charge-cutting function within a wrapper that allows for differing cut methods to be selected).