Update delete contact functionality

[CJ-Lee01]

closes #13

[wamps-jp]

Seems okay. I think the usage of Object selector might be a bit questionable (as in it might create complications later) but for now it's fine. Just noting that for future edits, if ever.

[CJ-Lee01]

I agree that the selector being of type Object is somewhat questionable and should be somewhat changed in the future.

I wanted the selector to have either type Index or type Id but Java doesn't allow a variable to have multiple types.

I wonder if there is a way to strictly enforce that the selector is only used for the equals method, was thinking if I should wrap it in Predicate<Object> or Predicate<?>.