Allow for unhooking of actions in bbPress class

[johnjamesjacoby]

It's currently impossible to unhook any of the bbPress class's actions. Even though they are public, they are not static and rely on the use of:

add_action( 'foo', array( $this, 'method' ) );

The problem is the use of $this. Only the bbPress object is aware what $this is. Plugins that may want to unhook or replace certain core functionality cannot manipulate them. A new action that passes $this should do the trick.

(In [3692]) Add 'bbp_after_setup_actions' action to bbPress::setup_actions() to allow class actions to be manipulated. Fixes #1730.