Send ext mods better

This changes the way ext_mods are sent again, I tried to be clever in the last 2 iterations but that proved to be a problem. fortunately the last 2 iterations did simplify the code and opened up a lot of possibilities, they were still great additions tot he underlying flexibility of salt-ssh!
This PR makes the ext_mods get deployed in much the same way the thin tarball is, the ext_mods are also versioned so they only get deployed when they need to be.