VitalSigns: add some validation

git-svn-id: https://markus.cdf.toronto.edu/svn/csc207-2014-09/group_0909@26 8153ec5e-17d7-4962-8641-23ff7c14a8d4
add Javadoc to InvalidVitalSignsException

git-svn-id: https://markus.cdf.toronto.edu/svn/csc207-2014-09/group_0909@27 8153ec5e-17d7-4962-8641-23ff7c14a8d4
change float to double, implement 1 test

git-svn-id: https://markus.cdf.toronto.edu/svn/csc207-2014-09/group_0909@28 8153ec5e-17d7-4962-8641-23ff7c14a8d4
complete VitalSigns tests

git-svn-id: https://markus.cdf.toronto.edu/svn/csc207-2014-09/group_0909@29 8153ec5e-17d7-4962-8641-23ff7c14a8d4