gmail-to-drive-by-labels adds new content to the bottom rather than top of document

[don-petry]

When gmail-to-drive runs, it is appending the email content to the document rather than pre-pending. This forces the consumer of this content to scroll to the bottom of the document for the most recent and relevant content.

• Add rule to specifications, tests and implementation that newer content should be added to the top of the document (prepended)