Making the JSON example complete as though you were reading the raw headers themselves in the email's source

Adding an explicit example, and also telling developers the headers will be STRIPPED FROM THE FINAL EMAIL and to not expect the headers to be visible in the email's source upon receipt.
Merge pull request #663 from sendgrid/develop

Ben is the right name 😍
Items 204, 207, 213 & 215
Updated file paths
Added an index.html for the VidGrid > Event Notification App directory
fixed file path for marketing_email_setup.md
Added an index for VidGrid > Marketing Email
Rename source/API_Reference/Webhooks/index.html to source/API_Reference/Webhooks/glossary/event_webhook.html

442
Merge branch 'develop' of github.com:sendgrid/docs into develop
added index files to 4 vidgrid > marketing email app> sub directories
fixed _config.sample.yml
Update email_templates.md

Added warning at top - availble for Silver or higher
Task 469

"Make an info block at the top of the page (see descr)
Should say ""This App is only available to Silver accounts and higher""

Link ""Silver and higher"" phrase to https://sendgrid.com/pricing"
Task 475

"Make an info block at the top of the page (see descr)
Should say ""This App is only available to Silver accounts and higher""

Link ""Silver and higher"" phrase to https://sendgrid.com/pricing"
Task 329

Link to Bounces:
https://sendgrid.zendesk.com/hc/en-us/articles/200181478
Update email_templates.md

Adding info block at top - available for Silver or higher
Task 459a

"Make an info block at the top of the page (see descr)
Should say ""This App is only available to Silver accounts and higher""

Link ""Silver and higher"" phrase to https://sendgrid.com/pricing"
add vagrant for better development exp
Create feedback_loop.md

Created glossary page for Feedback Loop
Updated broken file paths