Created 'get_xyz' fns, replaced 'import *' in 'train.py'.

[borgesa]

Hi @victoresque ,

I added three get functions:

• 'model.model.get_model_instance'
• model.loss.get_loss_function' 'model.metric.get_metric_functions'

These replace the 'import *' instances in 'train.py' and makes the code easier to read.

Further, the update aligns better with the 'best practice' of Flake8 rule F405.

Let me know if you believe I should update/change something.