Error Model Choice Argument for Dose-response Model Fitting

[sedavid01]

Goal: Add an argument that allows users to choose between the t-distribution or normal-distribution assumption for the dose-response model fitting.

• Allow for users to have the option to choose different error distributions (for now, just t- and normal- distributions)
• Default error distribution should be t-distribution (as-is)

[sedavid01]

Attaching testing code, please note that it is saved as a txt file. code_testing_updates_in_er-distribution.txt

[sedavid01]

The pull request for this ticket was merged into 'dev'. Closing out this ticket.