add PhysicActionTestCase, SetMassActionTest

added BaseClass for PhysicActionTests and setMassActionTest
modified setMassBehavior - now zero mass is a valid input
deleteTestProjects, SetMassActionTest structure
deleteTestProjects -> PhysicActionTestCase.tearDown()
physicobject -> physicsObject
add empty lines -> SetMassActionTest structure (makes it more readable)
init - act - test

PhysicActionTestCase -> PhysicsActionTestCase