Reimplement average relapse duration with setting

[cubandle]

• Reimplemented Recent Average function (closes #79)

• Added setting to customize how many recent attempts to consider (0 to disable)

• Modified Date format setting to show current value:

[KiARC]

There are some merge conflicts I'll have to sort out but this looks good!

[cubandle]

Sorry about the merge conflicts, I just rebased to fix them. I will also fix the merge conflicts on the other PR once this one is merged