Mllibs

General update

- Multiple updates to library

- Added the ability to store machine learning models using <code>nlpi.store_model</code>
- Renamed <code>nlpi.store</code> to <code>nlpi.store_data</code>

- Added new module <code>sltree</code> (DecisionTree models)
- Added new module <code>slcatboost</code> (Added CatBoost models)
- Both modules are utilised with base class <code>eval_base</code>

- Added cross validation & train-test splitting evaluation class `eval_base`
- Added gradient boosting machine learning evaluation class `slensemble`

- Added new module for linear regression and classification models <code>sllinear</code>
- Added new module for dimensionality reduction using decomposition and manifold learning approaches <code> usldimred</code>
- Added **NER** based sentence splitting for more accurate request interpretation
- Updated **mllibs** design (calmer colours)