Placeholder for PRs regarding identity spec

[turt2live]

This is just a tracking issue for myself, and maybe people who review the PRs.

High level PRs:

• Deprecate the v1 IS API and replace most of it with v2 #2254 - Mirror v1 to v2 where behaviour is unchanged (aside from auth). Covers part of MSC2140.
• Spec the v2 IS auth APIs #2255 - Actually define auth for identity servers. Covers part of MSC2140. Refer to MSC1961 (excl) when in doubt.
• Spec IS terms of service #2258 - Define terms of service handling. Covers part of MSC2140. Will probably be based upon PR2, and might be best to just merge them together.
• Remove bind_* params on /register as per MSC2140 #2279 - Remove bind_msisdn and bind_email from /register. Covers part of MSC2140.
• Spec client-server IS unbind API #2282 - Define new unbind endpoint and behaviour from MSC2140 (last 2140).
• Spec m.identity_server account data #2281 - Introduce storing IS in account data. Covers MSC2230 (excl).
• Spec the v2 lookup API #2287 - Introduce new lookup endpoint. Covers MSC2134 (excl).
• Deprecate id_server and make it optional #2310 - Deprecate id_server in requestToken. Covers MSC2263 (excl).
• Point to the new v2 identity endpoint #2304 - Fix isvalid (and other v2) references for third party invites, etc
• Spec MSC2290: 3PID binding split #2328 - Add new add/bind endpoints for 3PIDs. Covers MSC2290 (excl).

Note: MSC2264 (excl) requires no spec changes.

[turt2live]

The remainder of this is blocked until 2290 decides if it is obsoletes 2263 or not.