Update our high-level architecture diagrams

# Problem

It would be good for new hires to have a set of diagrams to introduce them to the very high-level architecture of the Hypothesis system. As far as I know the latest high-level architecture diagrams that we have are those created by Nick back in 2017 (pre-LMS app!): https://docs.google.com/document/d/1saDTLAniQiwV3KlUE7imo1ZP2BVSVEOQm_yfbKbCKn4/

# Solution

We should produce an updated set of high-level architecture diagrams based on the old ones.

From conversations with the team I gather that people think it'd be best for these to stick only to the high-level: the different apps and services and how they connect with each other, and not the details of how each app's code is structured internally.

Also from conversations with the team I gather that people think it'd be best not to overload new contributors with too much information up-front so the architecture diagram needn't actually cover _all_ our apps. h, client, LMS, Via and Via HTML are core and should probably all be covered. But bouncer, Checkmate, h-periodic, and things like our Python libraries and developer tools can be omitted.

Slack thread: