Allow skipping the md5() on the email address value in the Gravatar helper

This is useful for web services which pass the gravatar hash but not the
original email address of users.
Merge branch 'hotfix/4522' into develop

Forward port #4522
Updated Gravatar helper to use auto-detection for pre-hashed email addresses
Revert code formatting on array in Gravatar helper
Merge branch 'hotfix/4523'

Close #4523
Merge pull request #4526 from Slamdunk/em/id-on-static

Fill SharedEventManager events with identifiers
Merge branch 'master' of github.com:zendframework/zf2 into hotfix/mvc-suggest-dependencies
Merge branch 'hotfix/4526' into develop

Forward port #4526
Merge branch 'hotfix/4526'

Close #4526
Merge branch 'hotfix/4523' into develop

Forward port #4523
Merge pull request #4528 from bakura10/fix-aggregate-hydrator

Fix priority not handled in AggregateHydrator
Merge branch 'hotfix/4528'

Close #4528
Merge branch 'hotfix/4528' into develop

Forward port #4528
Merge pull request #4529 from sjuvonen/master

Allow Zend\Form\Element\Checkbox to return real value instead of always a boolean
Merge branch 'hotfix/4529'

Close #4529
Merge branch 'hotfix/4529' into develop

Forward port #4529
Move more dependencies from 'require' to 'suggest'
Merge pull request #4421 from samsonasik/fix/docblock.Zend_

fix docblocks : "Zend_" should be "Zend\" and some typos
[#4421] Fix unit tests

- Since class name listed in exception changed, expected exception message
  needed to change
Merge branch 'hotfix/4421'

Close #4421