Add Software Bus Structures Reference Diagram to Doxygen Users Guide

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The attached SB structures reference diagram should be made available in the user's guide.

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Imported from trac issue 181. Created by sstrege on 2017-03-01T14:25:08, last modified: 2019-07-03T12:48:08

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Trac comment by sstrege on 2017-11-17 14:13:37:

Diagram needs to be updated to include expanded APID name space structures

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Trac comment by jhageman on 2019-07-03 12:48:08:

Moved unfinished 6.6.1 issues to next minor release