"Connected to group" activity should be sensitive to post_status changes

[boonebgorges]

As of 515a923, connecting a paper to a group will no longer create activity items in the corresponding groups if the paper is a draft. However, this means no "connected to group" activity is created in the following case:

1. user creates draft paper, connects to group
2. later, the user publishes the paper

There should be something hooked to transition_post_status or something like that, which fires off cacsp_create_added_to_group_activity() as needed.