remove old code that has been incorporated in the main code base

(native to python callbacks commit #e85f6b0)
create an extended pyPot which can return the potentials simulation

includes a build script
update proxy to design used for a working ensemble potential
update test case to create ensemble simulation with 3 members
initial implementation that can be called by xplor
update to call calcEnergyAndDerivs of ensembleProxy
add code to call into energyMaybeDerivsX via the proxy
remove redundant call to calcEnergy on the proxy
proxy now registers to the simulation upon creation
update to call cython callback function

note the callback is in python 'space' and so needs to acquire the gil,
this is almost immediately released again... as the python function will
then call a 'nogil' cython function/method
add callbacks to calcEnergyAndDerivsMaybeX where X=0-4
cleanup
unregister simulation when complete