Add guide on high level Trinity architecture

[cburgdorf]

What was wrong?

The documentation is lacking a high level architecture guide for Trinity (e.g. explain layer, processes and other core things)

How was it fixed?

Wrote such a guide.

Teaser

Known issues:

• the graphics aren't that professional. I'm not a designer and these should act as stubs until someone who knows this stuff steps in
• still missing plenty of things that would fit into the topic
• links to some APIs don't work yet because we don't have them in our API docs yet
• links to some Python APIs don't work yet because I assume we need to configure something for that)

Cute Animal Picture

[carver]

links to some Python APIs don't work yet because I assume we need to configure something for that

Which python API reference is not linking as expected? Intersphinx is set up correctly for linking out to python, afaict.

[cburgdorf]

@carver turns out I just had the linking syntax wrong. Links to BaseManager and BaseProxy are now working as intended.