Add TweetLoader Class

[dieko95]

As a user, I want to use a method to query `angostura.tweets` 
by batch size and batch number,
and have as output these tweets as `tf.dataset` type. 

About this Class

This class is an abstraction of AngosturaConnection. The method is to be implemented it as a generator. The user just uses it in a for loop.

Purpose

Perform query paging to return batches of tweets that will be consumed the vocabulary modules.

Parameters

• Batch Size, Batch Number

Returns

• tf.dataset.

Tasks

• [x] Create TweetLoader class.
• [x] Integrate AngosturaConnection within the constructor.
• [x] Create load_sinluz_rawtweets method.
• [x] Logic that converts parameters batch size and batch number to SQL query.
  • Sort it descending by timestamp of the tweet.
• [x] Return tweets as a tf.dataset.
• [x] Create respective test.