NewCard: Enable attachment of PDF version of email

[mrk3767]

Problem

When used for personal use, the attached permalink to the email is sufficient. If the card is viewed by someone else, however, there's no way for them to open the email that is contained with in the creators account.

Solution

1. Get a download link to a PDF version of the thread
2. Attach PDF to the new Trello card
3. Show a checkbox to enable/disable PDF & link attachment functionality
4. Save checkbox options in user properties