local commit to ensure i have a rollback point for debugging

trying to fix some spurious ARP error that came about just renaming applseed.primary_trees
new mtree files and doc files
support installing backup trees, cleaned up deprecated variables
fixed bug with installing primary trees bottom up

bug was error installing PrimaryTree b/c assumes leaf nodes are all at the same level, debug the error
early support for activating multiple backup trees

(1) early support for activating multiple backup trees
(2) fixed an issue that allows a switch to have an adjacent host in the tree and an adjacent switch in the tree (making the switch a leaf node and a non-leaf node)
(3) hard-coded tree and backups for H6S9
documentation figures, mtree and measurement files for H6S9, and mininet script to use NetworkX
H6S9, H4S8 support and scapy script
cleanup and started implementation of new setup for triggering Primary Tree installation

tried to implement primary tree installation trigger such that a ping to  a special address (10.99.99.99) would result in the packet arriving at the controller, which would start the primary tree installation
minor edits to mininet scripts