Change class and file names to CodeIgniter standards

change all model classes to match Codeigniter standards
change DocumentListMapper to match CodeIgniter standards
Edit Document_model

fix references to Abstract_base_model
remove require_once('Person.php')
remove obselete functions setId and getId > these
are already defined in Abstract_base_model
Add User_model

Add User_model as subclass of Person_model
User_model provides additional attributes: username, aaiId and role
getters/setters for these attributes
Add FIXME comment

add a comment to the method iterateVisible > should not
call echo in models!