Change the TrainableModel::summary API to return `ModelSummary`

In current implementation the TrainableModel::summary return the list with the descriptions for the following layers.

This information is readable but doesn’t allow for easy transformation of model summary gathered data as it is give as raw String. Additionally, the implementation classes log the provided layers description in more readable way, but it is only printed on stdio and not available at least as pretty formatted string that could bu printed later. The problem is more annoying in jupyter notebooks where we don’t have an access to stdio and so the logged pretty summary is not visible.

I would propose creating some simple ModelSummary data class that would be responsible for holding the model summary data and would have some good implementation of toString() method that could be easily printed. It would allow for creating custom printing methods for ModelSummary as well as good keeping of model summary data as a single object instead of List<String>

[zaleslaw]

Hi, @knok16. Give me a few days to think about it; I’ll return to you in a couple of days.

[zaleslaw]

I’ve checked the 0.3.0-alpha-4 artifact, print summary works as expected and this issue has been fixed.