Bug 957894 - Pre: Remove outdated comments.
Bug 957894 - Part 1: Add fxa account pickling code.
Bug 957894 - Part 2: Test AccountPickler.
Bug 957894 - Part 3: Pickle on sync.
Bug 957894 - Part 4: Unpickle in accountsExist.
Bug 957894 - Part 5: Add deletePickle test.
Bug 957894 - Part 6: Delete pickle when removing account.
FOLD: Add FXA deleted account receivers.
FOLD: Broadcast account deletion.
Bug 957894 - Post: Remove unused imports.