Working 10GbE! (tested with tut2)

Created two directories of hdl files for code that has changed between
virtex 6 and kintex 7.

yellow block constructor now attempts to call a factory method when
initialising, allowing different subclasses of yellow blocks to be used
for different platforms. This is done for the ten_gbe_v2 yellow block
class.

10gbe tested with roach2 tutorial 2 (I was manually setting the arp
table, need to check tap_start works properly).

note: I changed hdl_sources/kat_ten_gb_eth/wb_attach.v because the arp
table wasn't being written correctly. TODO: work out why the old code
didn't work...

edit: Tested with tap_start and no manual arp intervention. Works fine.