Feature: Add pump battery

[mjliedtke]

For those of us still using an old Medtronic, it would be nice to be able to see the battery percentage in Information Display and be able to set in the alarms. I'm happy to take a stab at it if you would like.

[bjorkert]

Hi, thanks for posting. Pleas do! Let me know if you have any questions before starting.

[mjliedtke]

PR #481 created for dev. Let me know what you think. You won't hurt my feelings. :)