🎨  X-Frame-Options SAMEORIGIN
🎨  X-Frame-Options SAMEORIGIN

refs #230

- change x-frame-options from DENY to SAMEORIGIN
- SAMEORIGIN: This setting will allow the page to be displayed in a frame on the same origin as the page itself.
- background: if we deny x-frame-options, we can't export content/database

TryGhost/Ghost-CLI,TomChantler/Ghost-CLI