Calculate IC50 and verify against PRISM's value

[TKMarkCheng]

Is your feature request related to a problem? Please describe.
A natural extension of this project - doing the IC50 for the user without the need of PRISM.

Describe the solution you'd like

1. Uses a correct curve fitting tool - currently on PRISM the 4-parameter logistical fit curve is used (https://www.mdpi.com/2409-9279/1/1/8)
2. Plot all curves for visualisation, and flag outstanding values (IC50 outside the upper/lower detection limits)
3. Return IC50 to table according to user-defined groups (V2.0)

[TKMarkCheng]

A good package to use is the drc package