Create grid in admin that shows batch information

[agustinbv]

Basically, the idea is to create a grid that shows the following information about batches sent to Mailchimp:

-ID -Mailchimp Store name -Status -#Carts -#Customers -#Orders -#Products -#Subscribers

New and modified items will be shown separately. It remains to be seen what exactly to do about items which aren't synced (with errors)