Plotting functions updated

1. Predicted & observed lambda are recorded and plotted, instead of
abundance & scaled lambda.
2. Plotting functions are fixed so that now the generic function
plot_obs_pred takes in the axes object, not figure object, to facilitate
calling macroecotools.plot_color_by_pt_dens.
Remove unnecessary module dependency

With theta_epsilon moved to mete_distribtuions, module EM_dist is no
longer needed.