Add hit location HP equals total HP mode for hit locations

[The-Axel]

What: Describe the bug

A Gorp (or any other creature with only one hit location) should have it's full hit points in its hit location.

How: To Reproduce

Steps to reproduce the behavior:

1. Go to Hit Locations
2. Go to Gorp
3. Create an Actor
4. Drag Body onto Actor
5. Hit Points use the Abdomen calculation.

Expected behavior

HP for the location = Total Hit Points.

Suggested solution

Add an option to the "For damage calculation, act as" dropdown of Total Hit Points.

[wake42]

The "For damage calculation, act as" field does not affect the number of hit point, and the one hit location Gorp is an exception to the general rule of how hit locations work. For the moment at least I made the call that it's not worth to complicate the calculations to include a separate model of hit location hp calculations just for one hit location creatures, but eventually I might reconsider.

I did update the documentation page about hit locations to try to explain how it's supposed to work: https://sun-dragon-cult.github.io/rqg-system/items/hit-location and I included a note about the "Gorp edge case".

I'll reformulate the issue title and put it into the backlog for future consideration, but realistically I think it will get quite low priority.