Update the high level diagram of Stonesoup

[cmoulliard]

Proposition

As it seems that the following diagram is not up to date, I propose that we review and update it:

Part of the revision process, we should:

• Version the diagram like also include the github tag/release or commit sha link to be sure that it matches the last stuffs released
• Include a hyperlink top of each system component to point to the github repository hosting the code. If not possible, add text under the paragraph high level architecture
• Interaction between the system components should be represented to have a better idea about which component if the entry point (= aka master), which ones are the children
• Define where we will maintain the high level diagram

[ralphbean]

Back in 5ec5ef4 we just dropped the diagram rather than improve it.