MtpA - All changes relating to JUnit testing on UserMarker

Changes -

MainActivity - try/catch around UserMarker builder
UserMarker - add validation calling LiftMeDataValidator
LiftMeDataValidator - new class with validation methods
DataValidationException - new custom exception for the above
TestLiftMeDataValidation - JUnit test for LiftMeDataValidator methods
TestUserMarker - JUnit test for UserMarker builder