Cf/clean models

[CarolinaFurtado]

Small changes to the code, including extra verifications and new functions

Verifications:

train: if no dataset exists, gives error

train: if no pretrained model exists, gives error

train thresholds: if no model exists, gives error

train thresholds: if no datasets exists, gives error

plots ok

right model selected - yes

no image but it selects the right model depending on the model name

all workflowsteps work? yes

train

train_thresholds

test

[CarolinaFurtado]

Awesome! I'll look over and make the changes tomorrow! Thanks!