Hookify Zotlabs\Daemon\Master::Summon

Create a hook for Master::Summon() to allow interception of tasks that are sent for background processing (for example, by the queueworker experimental queue processor).

Because Summon() kicks off a new php process to run the "Release()," system can have it's memory overwhelmed and begin to thrash in certain circumstances where a massive number of background requests are made in extremely quick succession. With this change, the updated queueworker addon will intercept the Summon() request and add the task to the queue of commands to be processed in a more controlled way.

ALSO: make the location of the php binary able to be set as a configuration variable in case it is not in the PATH of the user (or a different version needs to be specified for example on a server that has multiple PHP versions installed).