Added Design Directory

I added a design directory where software design flowcharts and documents should go. I included Tyler's design as well. In this design, the squares are nodes, the circles are topics. It is color coded for the different types with blue being input, green navigation, dark green output, and red for debugging. 

Note that red are topics only used for debugging, normally the debugger will listen to all topics, but that would get messy on this diagram.