<iframe> Support

[A-Paterson]

Currently, Net Doc breaks if embedded in an <iframe> tag, which has caused problems with the Net Doc Desktop tabs implementation and means it can't be embedded in Teams.

[Arcath]

Was this a CORS issue? Might be something we can fix with the nginx revese proxy we use after #42

[A-Paterson]

The console shows this:

Request URL: https://docs.lhs.lancs.sch.uk/app
Request Method: GET
Status Code: 403 Forbidden
Remote Address: 20.199.107.83:443
Referrer Policy: strict-origin-when-cross-origin

Request URL: https://docs.lhs.lancs.sch.uk/app/login
Request Method: POST
Status Code: 302 Found
Remote Address: 20.199.107.83:443
Referrer Policy: strict-origin-when-cross-origin

A warning has appeared next to the cookie in the response.