[metalearn] add more feature to task state

[cosmicBboy]

The metafeatures used by the controller are currently very limited. Implement the following metafeatures:

• scorer encoding: one-hot encoding of scorer in distribution of scorers
• task type encoding: BINARY, MULTICLASS, etc.
• number of categorical features
• number of continuous features
• metafeatures specified in Supplementary Material for Efficient and Robust Automated Machine Learning