Add CategoricalCrossEntropy and gaussian noise sampling to Bolton Implementation

[changliu-gp]

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[changliu-gp]

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[changliu-gp]

includes:

• block in optimizers/get_noise to get gaussian noise
• new parameter "delta" to functions
• 2 new test cases
• example to use gaussian noise in tutorial
• new class for categorical cross entropy in losses.py
• new test cases for categorical cross entropy in losses_test.py