Medical Treatment - Add treatment time multipliers & restructure settings

[pterolatypus]

When merged this pull request will:

• Add multipliers to treatment time based on medic level for all treatments whose base time is currently configurable
• Move medical_treatment settings to their own category, as the other was getting a bit full
• Move treatment time settings to a "tweaks" subcategory for tidiness
• No change to bandages yet but I'd like to include them

I'm torn on whether it makes more sense to have one category for the whole component like this, or separate all the medical settings into a normal and "advanced" category for all this fine-grained stuff that most people won't bother changing.

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