General callbacks registration

[bergie]

Currently callbacks to Midgard signals in MidCOM are done by various libraries directly. However, it would be better to handle callback registration as a service that could be configured using normal MidCOM configuration stack.

http://www.midgard-project.org/documentation/php_events/

Something like:

events:
  - 
    class: *
    event: action-update-hook
    callbacks:
      - 
        class: universal_handler
        method: something_was_updated
        additional_parameters: []
  - 
    class: midgard_article
    event: *
    callbacks:
      -
        class: universal_handler
        method: something_happened
        additional_parameters: ['midgard_article']

(copied from http://trac.midgard-project.org/ticket/1278)

[bergie]

We should also look at how observation is done in PHPCR: http://www.day.com/maven/jsr170/javadocs/jcr-1.0/javax/jcr/observation/ObservationManager.html

[bergie]

Here is an example of registering observers: midgardproject/org_midgardproject_projectsite@f4022f0#diff-1