Improve example scripts

[NicsWorld]

This pull request improves the example scripts in a few ways:

Avatars:

• Handled the promise returned by moov.avatars.get(UNIQUE_ID) by awaiting it
• Wrapped the code that loads the credentials and initializes the Moov client in a try-catch block to handle any errors that may occur.

Create Transfer:

• Added checks to ensure a matching payment method was found before trying to access its paymentMethodID property.
• Removed the unused transfer constant