chore(app): restructure mutations for better typing/naming

[michael-small]

As I looked over the app examples for writing the documentation, I noticed two things that could be improved for clarity now that best practices have been hashed out more.

• Typing: Rather than explicit types in the function's generic params for httpMutation, it is better to be typed with:
  • the parameter type in the actual request parameters
  • response in the response callbacks and/or parse.
• Naming: the example for the standalone functions for mutations was made with rxMutation in mind, but ended up encompassing httpMutation too