Move Registration related methods out of User model into a module
Add url_identifier tests to User unit test.
Add Exercise Unit Test for relationships and validations.

Chart related methods will be moved out of the Model so no tests
were added for those.
Add Unit Tests for Exercise Intensity, Location, Satisfaction for relationships
Add Unit Tests for Headache Related Models

Headache
HeadacheDuration
HeadacheSeverity
HeadacheWarning
Add Unit Tests for weight related models.

Weight
LoggedWeight