Design/architecture doc touchups

[sthetland]

Three minor but possibly portentous changes:

1. I just wanted to move the architecture diagram up on the page, for a high-level first view of the architecture.
2. Changed the term "processes" to "services", as they are called in the console. We should propagate this change throughout the docs, but this page is a start.
3. Added as a touchpoint for the conceptual information a reference to the console UI where the concepts surface. Other pages and concepts should similarly aim to anchor concepts and ideas and how they are framed to the Druid console UI.

[techdocsmith]

Minor comment on style