A Classification Example in Forte Pipeline

**Is your feature request related to a problem? Please describe.**
Provide Forte with a classification example

**Describe the solution you'd like**
1. Using the reader to parse the dataset as Sentence Datapack and Token Datapack

2. Using the Text Extractor on the input to Build the word embedding table from a Token level and using the Attribute Extractor again on the output to get the label information from the Sentence Level.

3. Build a CNN and a Bert sentence classifier for the sentiment classification task on the IMDB movie review dataset.
(https://www.kaggle.com/lakshmi25npathi/imdb-dataset-of-50k-movie-reviews)

**Describe alternatives you've considered**
Attribute Extractor in the output maybe replaced by other extractors.

**Additional context**
View the idea design at:
(https://drive.google.com/file/d/17kcwu-XOVzk-8lEmVDWWASuAohPIA-PQ/view?usp=sharing)