Add ability to change equipped pet

[wesleypayton]

Problem

As a user, I am able to change what pet I have on my island by selecting a different pet on the pets page

Definition of Done

• User can navigate to pets page and tap a pet they have unlocked to equip that pet
• Currently selected pet is stored and accessed through the CurrentUser's CurrentPet property
• User's currently equipped pet is the pet that is displayed on their island

Subtasks

• Examine how pets are currently handled by timer page, pets page, and database
• Implement functionality to update database when user selects a different pet
• Add logic to timer page to display pets according to what user has equipped
• Documentation and Testing