Collapse prep/write steps in model evaluation

[vineetbansal]

Consider merging:

In general, the plot* scripts could take the output of Snakefile_data, Specific examples:

• write_outcome_distr and calculate_outcome_distrs could collapse
• prep_nn_tc/write_nn_tc/plot_write_nn_tc
• any others you can think of.

[anushka255]

This issue has been dealt with. Thanks!