Standardize some BAC methods

[prioux]

In the BackgroundActivity core class, provide the following base methods:

def failed_items
def successful_items
def remaining_items

We already have the following helpful methods that can be used to implement them:

def selected_items_from_nil_messages
def selected_items_from_present_messages
def selected_items_from_messages_matching(regex)

These last three method should become protected, and the main methods of this issue (failed_items, successful_items and remaining_items) will become the real interface.

Subclasses can overrride them or simply invoke the appropriate selected_items_* methods.

By default (because it's the most common situation), failed_items will just invoke selected_items_from_present_messages and successful_items will invoke selected_items_from_nil_messages.

The method remaining_items is always just what's not yet processed, so the tail end of the items list.

• Add methods
• Adjust all subclasses, as necessary (only those that don't follow the "NIL message means success" convention)

[prioux]

We could then add a method

def reset_failed_items!

which would prune the items list of anything correctly processed, and leav only the failed ones

Also, the "retry" mechanism could be adjusted to use these methods now.

[prioux]

Huh, I think I already implemented all this!