Unblock fix for failed app installations and reading Pebble ID from the environment

Apologies for not breaking this apart in to two pull requests; git is not my first language. :)

The changes to pebble.py address what happens when the number of installed apps reported is larger than the number of full resource description blocks available in the app bank. Instead of crashing in that specific case, a warning is raised (with the trailing data for later analysis) and the operation continues. I tested this with some older applications (no UUID) and was able to work normally - without this change, any attempt to modify the app bank crashes as the app bank list function is called before any app bank operations.

The change to p.py (and associated README.md changes) simply read from PEBBLE_ID if it is present and if no pebble-id argument is provided - this lets users set it in their bash_profile (or equivalent) and then omit it from future use of p.py.