Resolve "Create a tab for login and a database for User Information"

Closes #22 (closed)

Changes:

• Creates tab4.py, for the Subscribe function as shown below: Has placeholder functions for the Subscribe and Login functionality. Implements the checkbox which returns 1 to var1 when checked and 0 when not checked.
• Change in Database.py to create table Users with the columns UserID, UserEmail and Notifs.
• Change in tab3.py is cleanup as add_to_database function is complete (removes comment).
• Change in GUI.py is to create tab4 in the GUI, extends the window of the GUI by 100px in order to display the entirety of tab4 without the user having to manually extend the window.
• Updated README.md to cover the changes made in this ticket.

Testing:

• Window displays as expected
• dummy user email sampleuser1@gmail.com appears in FamousQuotes.db