Allow users to change model names

[Firenze11]

Summary

Currently the model legends in PerformanceComparisonView shows "model_0", "model_1" etc which might be hard for users to distinguish between models.

Possible Solution

• Make the legends in PerformanceComparisonView clickable, and becomes a text field where users can type model names in
• Also change the model identifier in column names, e,g, currently we have @score:0, which will be changed to @score:xgboost_model or the like.