Add various improvements to my_activity.py

* convert diagnostic prints to logging
* add -v and -q options to control logging verbosity
* add -d option to fetch patchset data
* add format values:
      (issues, changes,reviews)
  - {created}: the date an activity was created
  - {modified}: the date an activity was modified
  - {status}: a status indicator for the activity
      (changes,reviews)
  - {activity}: a count of the number of comment interactions
      (changes)
  - {delta}: for changes, the number of lines added and removed
* use a default formatter for outputting that skips, rather than
  chokes on, missing values.

Change-Id: Ib50c8c72b98b8ef5939d59ab93c5fc0a1a49599f
Reviewed-on: https://chromium-review.googlesource.com/451278
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>