Implement commands and UI for producing labels using Mail Merge. 

Behind the scenes this is implemented as Table with the proper number of table columns and rows, and eventually (depending on the setup) NEXT field (https://support.office.com/en-us/article/Field-codes-Next-field-3862fad6-0297-411a-a4e7-6ff5bcf178fd?ui=en-US&rs=en-US&ad=US) - so this will eventually require implementing NEXT field.

Note: In MS Word, this is in Mailings -> Start Mail Merge -> Labels...