Merge branch 'normalize-forwarded-emails' into 'master'

__tests__/files/gmail-gmail/chrome-chrome/17/received.eml

__tests__/files/gmail-gmail/chrome-chrome/17/sent.eml

__tests__/files/gmail-gmail/chrome-chrome/README.md

__tests__/files/gmail-outlook/chrome-chrome/17/received.eml

__tests__/files/gmail-outlook/chrome-chrome/17/sent.eml

__tests__/files/gmail-outlook/chrome-chrome/README.md

__tests__/files/outlook-gmail/chrome-chrome/17/received.eml

__tests__/files/outlook-gmail/chrome-chrome/17/sent.eml

__tests__/files/outlook-gmail/chrome-chrome/README.md

...sts__/files/outlook-outlook/chrome-chrome/17/received.eml

__tests__/files/outlook-outlook/chrome-chrome/17/sent.eml

__tests__/files/outlook-outlook/chrome-chrome/README.md