Copy link

[wetoolaguer]

This PR adds the ability to copy the secret's link instead of sending the email. https://www.pivotaltracker.com/story/show/166277253

Tasks:

• [x] Add toggle for switching between send email and just copy link in create form
• [x] Handle sending email / generating copy page in controller
• [x] Fix dashboard secret-item to display 'copied links'
• [x] Add tests

Screenshots:

• New secret form with option to toggle email fields

• Copy page (only accessible once)

• Secret item view when not sent via email