Added employment

Added the employment table, which is a joined table for users and
departments.  This is a many-to-many relationship.  This table will also
store information about each employment.  Hourly rate, work study or
not, administration level.  The admin level will eventually become the
position description ID, but it can be used for this as well.  I don't
have the various views joined together yet, as I'm still learning about
everything.