Sanitize logging

[erikjohnston]

Related to: SYN-385 and SYN-388

• Log outgoing requests that use synapse.http.client.SimpleHttpClient
• Remove access_token's from logs:
  • synapse.http.server
  • SynapseSite's request's __repr__ and __str__
  • insert_client_ip (DEBUG logging) SQL logging is a generic problem here. See comments below
  • synapse.rest.client.v1.transactions {get,store}_response (DEBUG logging)
• Log the authenticated entity if one is associated with a request, e.g. the server or user.
• Improve request logging and remove twisted's logging:
  • IP modulo X-Forwarded-For
  • Query params (excluding access_token)
  • HTTP version
  • Response length

[erikjohnston]

This pulls in #185

[erikjohnston]

DEBUG level logging includes personal information, like access_token's and message contents. Should these instead be logged in some sort of TRACE level, though python logging doesn't have such a concept.

[erikjohnston]

This is ready for review: @NegativeMjark ?

[NegativeMjark]

LGTM