heartbeat 6.x-4.1

This release is the first release where heartbeat fungates as API and not as (POC) module with too many features and possible features.
Heartbeat activity streams are very customizable. We have attachments (comments, flags, ...) and lots of settings on a per-message basis to create the desired displays.
The views module would not be needed very much, but much work is to be one to take this beyond. Heartbeat comes with 3 default message access states, but other modules can add their own very easily. This way one can create displays in rather advanced user scopes. (E.g. activity within an organic group)