adding tadpoles to the EWSB eqs

Now they appear in the ewsb_step functions automatically at the right
place.
wrap long EWSB solution expression
simplify tadpole index expression
change tadpole sign convention to the one used in our paper

Convention:

  0 = d V / d v_i - tadpole[i]
update SMSSM EWSB solution
correcting general model name
define is_finite = false in case not tree-level EWSB solution available