Add a way to persist the count value

[itsnikhil]

Re-launching the counter app resets it back to 0. Find a way to save the value on Fitbit's local storage in order to persist the value. Submit a PR highlighting your changes.

Helpful resources:

• You will need a Fitbit account - https://www.fitbit.com/signup
• Fitbit simulator - WINDOWS or MACOS
• Open a Fitbit project in CLI - https://dev.fitbit.com/build/guides/command-line-interface/
• Fitbit docs - https://dev.fitbit.com/build/guides/file-system/#writing-a-cbor-file

[itsnikhil]

No problem @michaelliu23 someone else will take the issue