Social media image URLs should always use HTTP in emails

When a site running over HTTPS emails a receipt that contains social media links (templates/CRM/common/SocialNetwork.tpl), the link image src attribute uses the HTTPS protocol. Not all mailer readers will render an image over HTTPS (e.g., Outlook) and the user sees placeholders instead of links in the receipt. HTTP should be used for these images.

Background:
The SocialNetwork.tpl file uses the base URL $config->userFrameworkResourceURL. CRM_Core_Config::_setUserFrameworkConfig() forces $this->userFrameworkBaseURL to use HTTPS inside a SSL connection.