Added a calculated field named age to SiteUser. This field is not saved in the database but can be accessed from any instance of SiteUser.  Also, removed the StateLengthValidator that was at the top of models.py as it is defunct.
Added an 'age' field to SiteUser which will return the age of the user in years based on the user's date of birth.  Added a 'current_weight' field to SiteUser which will return the current weight of the user, in pounds.  Currently this property gets the users weight by querying the database for the most recent entry belonging to this user in the Weight table.  This might be changed in the future to simply be a stored field in the SiteUser table.  Then when the user enters a new weight on the front end the current weight field in SiteUser will be updated as well as a new entry being added to the Weight table.  Added a 'calories_burned' field to AerobicExercise. It will calculate the calories burned during that exercies based on the user's age, gender, weight, exercise duration, and average heartrate during the exercise.
Merge branch 'master' of https://github.com/CSc436/gymjournals into 81CardioAndAgeFields
Merge pull request #88 from CSc436/81CardioAndAgeFields

81 cardio and age fields
Merge branch 'master' into hzDisplayProfile