Additional exclusion parameters in activity loop

[r-a-y]

A lot of the really, cool GSOC ideas revolve around privacy and blocking.

For this to be effective with the activity component, we need to have better exclusion parameters to accomodate these potential features.

What we need are two additional parameters:

• 'include_author' - uses an IN query against the user_id column
• 'exclude_author' - uses a NOT IN query against the user_id column

[saurabhshukla]

Since, privacy is one of the fundamental concerns in a social network, I feel it should have an additional column in the activity table.

[r-a-y]

The 'filter_query' parameter in BP_Activity_Activity::get() can be used in lieu of what is suggested above.