Mutate Patch Action

[allison-li-1016]

Estimated review time: medium

Description of functionality: The PR adds a new action into Patch that converts all healthy tissue cells within a given radius into cancer cells.

Summary of changes: new Mutate action file

Discussion points:

1. I created this action to simulate a very specific use case for my T cells. Is it worth merging this into the main model? Do we see a functionality for this in the future?
2. Given the above point, should we add more functionality for this action? (e.g. "RATIO" parameter to convert a fraction of cells instead of all the cells, etc)

[kristaphommatha]

Looks great! I think it just needs some documentation and name changes for consistency.

[allison-li-1016]

@allison-li-1016 add some tests if we are going to merge it in