Add flag to turn on and off MailChimp's automatic google analytics tracking of links.

This allows campaigns to build more custom UTM_var combinations wihtout MailChimp clobbering them. It has been defaulted to not use MailChimp's automated service as none of our current sites will be using it going forward.
Start adding admin and object support for custom campaign variables
Build custom google campaigns if automatic tracking is off and analytics_utm_source is set.
Build a custom campaign from a config setting plus the user set one plus teh shortname (aka the date).
Use a shorter year string for the date used by the shortname.

This is because the only clients using Deliverance want the date strings formatted this way. It should probably be made more flexible in the future.
Make the analytics tracking ini settings live in the Deliverance section of the config settings

There is nothing to really tie them to MailChimp
Fix a variable name typo
Check utm_medium when trying to add utm_medium.
Return the sprintf directly, instead of reusing a variable
Merge pull request #12 from isaacgrant/custom-analytics-tracking

Support for custom analytics tracking vars on newsletters