Provide option for incoming heal text format

[Pahweh]

One thing I miss from vuhdo is how the incoming heal text works. In vuhdo, it subtracts the incoming healing from the health deficit, whereas aptechka just shows raw incoming. As a healer, its more helpful for me to see what the difference is to make better decisions about which heal to use. So for example:

• Tank missing 5k health with 4k incoming healing would show -1000 as the text, vs +4000
• Tank missing 5k health with 7k incoming healing would show +2000 as the text, vs +7000