Minor coding style
Instantiating central change executor to consolidate cron and api calls and behavior.
adding Update operation option to cron processor in mailchimp_lists
set update existing to true for cron processing of subscriptions so update operation will function
restructuring mc_lists_subscribe_form_submit to use mailchimp_lists_execute_change.
Comments & formattings
Adding capacity to process anonymous subscription requests in mc_lists_cron.
Restructured mc_lists_user_delete to use execute_change function.
Added interest group formatting to mc_lists_load_user_mergevars for cleaner code.
Abstracted out processing of subscription forms from individual form_ and user_ hooks.
Misc code style, comments, and typos.
Updated cron queueing functions to allow for anonymous items to live in the queue.
Rewrote mailchimp_lists_user_sync for clarity and to use the new execute_changes function.
restructured mc_lists_user_sync for clarity and to correct behavior for address changes.
Removing unnecessary warning message on newsletter form submission when an individual list was not altered.
Adding insurance against sloppy execute calls during cron processing.
Added support for groupings updates in cron-enabled lists.
Refreshing appropriate user list when the roles on a list are changed.
Tweaked list form for clearer and more elegant enforcement of Description character limit. Addresses #1930536.
Rearranged list form settings, fixed a display bug with interest groups options, added Form Label field to allow overriding the default label on blocks & forms.