[TIMOB-17290] UNIT_PT is missing in Ti.UI

Not that I use it, but the *Points* (pt) unit [mentioned in the docs](http://docs.appcelerator.com/titanium/latest/#!/guide/Transitioning_to_the_New_UI_Layout_System-section-30088148_TransitioningtotheNewUILayoutSystem-UniversalUnitSupport) is not in the list of UNIT_* constants, both in the documentation (http://docs.appcelerator.com/titanium/latest/#!/api/Titanium.UI-property-UNIT_CM) and [actual code](https://github.com/appcelerator/titanium_mobile/blob/e91102a8f8152a68dcb63115e09260be5f002f2c/android/modules/ui/src/java/ti/modules/titanium/ui/UIModule.java#L130-L134)