text: Title: Remove mutable arguments
  Body: As mentioned in openjournals/joss-reviews#1315, some functions have mutable arguments.
  
  I found the following instances of this:
  https://github.com/scikit-tda/kepler-mapper/blob/8a2a955e2b7302ee3c37e5c6a2c6ebfc1924a39b/kmapper/kmapper.py#L630-L632
  
  These could easily be transformed into something like
  ```
  def f(param=None):
      param = [] if param is None else param
  ```