Add departments, job groups and employee sqls

Adds the sqls for these tables.
Implement SQLModel classes

Adds the SQLTableModel and SQLQueryModel classes, which will be used to
display various generic models.
Working PayTypesDialog

Implements the models in the PayTypesDialog.
Create employee centre

Add the employee centre dialog box

Signed-off-by: Joseph W. Joshua <joejoshw@gmail.com>