Fixed: multiple instances of same class share computed.meta()

My last PR introduced a regression caused by the fact that Ember.computed() returns an instance of a ComputedProperty that is shared by all instances of a class where change-gated computed property is used.

This PR adds 2 new tests that test for this scenario and introduce a solution that passes these tests.
any reason for the `capitalize`? won't this clobber `property1` and `Property1`?