Added dynamic API snippets to cookbook (#1538)

* Fixed "How do I look at the intermediate data?"

* Fixed "How do I train a regression model?"

* Fixed "How do I use the model to make one prediction?"

* Small fix

* Fixed normalization examples

* Updated categorical examples

* Updated text example

* Updated CV

* Changed all the readers to mlContext.Data.TextReader

* Some PR comment fixes

* Updated static cookbook tests to match cookbook

* Added tests for dynamic API snippets, and fixed the bugs in md file.

* Cosmetic changes

* Addressed the final comments.

Author: Shahab Moradi