Refactoring AssignmentTeam and CourseTeam models

Created as an assignment for the CSC 517 Fall 2014 class at NCSU. 

*Assignment Details:*
E1452. Refactoring AssignmentTeam and CourseTeam models
Contact: Hamsini Bhoomi, hbhoomi@ncsu.edu
Classes involved: AssignmentTeam, CourseTeam, Team
What they do:
* The AssignmentTeam model checks whether a team has participants for an assignment, whether a topic has been picked by the team and reviews has be given for a particular team and adds, deletes and retrieves participants in a team.
* The CourseTeam model gives the paticipants in a course and allows to add and delete participants in a course. This is for the use by the instructor. 

What needs to be done:
* Check if we need two methods participant and get_participant as they may be similar. If so, refactor to make one method.
* Rename create_team_and_node method as create method (follow Ruby style)
* Rename includes? method to has_participant?
* Remove duplicate code from these 2 sublcasses of Team.
* Assignment_Team class too long (235 lines)