mailchimp 7.x-2.7

Fixes: SA-CONTRIB-2012-158 - MailChimp - Cross Site Scripting (XSS)

Changes since 7.x-2.6:

• #1781672 by stella: Ensure merge vars array exists before looping over it.
• #1787818 by marcvangend: Use list name as key in interest groups fieldset.
• #1194738: Add entity_token as a dependency to mailchimp_lists to enable user tokens.
• #1813096 by stijnd: Add campaig_id as return value for mailchimp_campaign_save_campaign.
• #1771964: Remove bundle keys from entity_info definition.
• Update existing webhooks to use revised mailchimp_webhook_key().
• Generage a private mailchimp_webhook_key().
• Properly escape the post type from a webhook ping.
• Required lists must have a role other than Anonymous selected validation
• #1700662: Fixed the 7202 update function