Starting the support of Safecracker Registration (@objectivehtml)

Still need a lot of work and probably a refactoring of Zoo Visitor support too, as those 2 guys are doing relatively the same things, but a bit differently… (make sense?)
Safecracker Registration (@objectivehtml) support

- Added hooks of SC Registration
- Get fields from channel (channel_name MUST be configured in the
config.php as $config['safecracker_registration_channel_name'] =
'my_channel';)
- refactoring a bit
Merge branch 'master' of https://github.com/experience/mailchimp_subscribe.ee_addon
Reverted necessary property declaration (ooops...)
Merge pull request #8 from pvledoux/master

Safecracker registration support, implemented by PV Ledoux.