Add plugin for getting tennis rankings, corresponding tests

[aaronmarm]

Adds a Tennis Rankings Plugin to Jarvis CLI

• When the word 'tennis' is mentioned in a query to Jarvis, it will enter the tennis rankings interface
• Within the interface, the user has 4 options, which they can select by entering the corresponding integer:
  1. Get the top 10 ATP (male) players: Calls API to get rankings, prints out top 10 WTA players
  2. Get the top 10 WTA (female) players: Calls API to get rankings, prints out top 10 WTA players
  3. Enter a new API key: The tennis data is taken from SportRadar, which requires an API key (can obtain a free trial)
  4. Exit the interface: This will cause Jarvis to revert to its normal 'Hi, what can I do for you?' prompt
• System is robust to bad input, will reprompt the user for what it is looking for
• All plugin functionalities are tested in the corresponding test file

Co-authored By: Julia Liu, Xuchao Zhou (Contributions removed in squash)

[pnhofmann]

Thanks!