Database basic user table and a post table

[AyrtonMiller]

This adds a python file defining the rudimentary tables of our flask database.

[huangyegithub]

This looks good. I think it is a great start. I may have some ideas of what to add later. I'll let you know when I have those sorted out.

[Bait1742]

1. Added tablename attribute to specify the table names explicitly, like "tablename = 'user'"
2. Specified foreign key relationship between User and JobPostings, like "user = db.relationship('User', backref='jobs')"