Automatically convert links to forms in interaction affordances and show deprecation warning

[benfrancis]

Some add-ons provide this manually and may also need updating.

See also #2806.

[benfrancis]

As far as I can tell mediaType is no longer added anywhere in the gateway.

The gateway automatically changes any use of mediaType in top level links to type.

Some adapter add-ons do provide their own links with mediaType rather than forms with contentType in interaction affordances, e.g. the Camera and VideoCamera devices in the virtual things add-on. Ideally this would be changed in the add-ons themselves, but we could try to automatically convert links in interaction affordances to forms:

• Change links to forms
• Change mediaType to contentType
• Remove rel
• (Probably shouldn't add an op member)

Trying to automatically convert add-on provided links to forms may be error prone, so we might want to consider just showing a deprecation warning instead.