Added MailAddressFilter extension point to mailer-plugin exclude email recipients
MailAddressFilter - Incorporated review comments from https://github.com/jenkinsci/mailer-plugin/pull/13
MailAddressFilter - Avoid use of MailAddressFilter.getDescriptor() which is not mocked test
MailAddressFilter - Updated comment to reflect switch to Describable/Descriptor
Merge pull request #13 from mudiobada/master

New extension point in mailer-plugin exclude email recipients