Preprocess: device.flashVersion, device.isMobile, device.language

[wesleytian]

Preprocess the following features:

• device.flashVersion
• device.isMobile
• device.language

1. Standardization: http://scikit-learn.org/stable/modules/preprocessing.html#standardization-or-mean-removal-and-variance-scaling

2. Impute missing values: http://scikit-learn.org/stable/modules/impute.html

3. Normalization: http://scikit-learn.org/stable/modules/preprocessing.html#normalization

4. Encode categorical features (optional): http://scikit-learn.org/stable/modules/preprocessing.html#encoding-categorical-features

5. Discretization (optional): http://scikit-learn.org/stable/modules/preprocessing.html#discretization

http://scikit-learn.org/stable/modules/preprocessing.html

[hrxiao]

Looks like a duplicate issue of #70