add new method for delegators

done:
* move delegator logic from create() to separate method
* remove automatic invokable service for delegator factories
* add delegator factory class validation
* update tests
revert test edits and add new tests
fix BC
add single delegator tests for abtract plugin manager
add multiple delegator test for abtract plugin manager
test cleanup
add delegator factory validation testing
add delegator from callback test
fix callback test
add callback support for delegator factories
code cleaning
Merge pull request #5175 from stefanotorresi/fix/pm-delegators

fix delegators to allow usage in plugin managers

Conflicts:
	tests/ZendTest/ServiceManager/ServiceManagerTest.php
Merge branch 'hotfix/5175'

Close #5175
Fixes #5172