NOTE: Task only necessary if we launch this as an A/B Test
####Background
We are planning to measure if we saw a 50% increase in app menu donations as measured by A/B test or pre-post analysis after moving the donate option as a part of Navigation refresh part 1.
####Task
[] Create a data controller in WMFData which outputs whether or not the user see the navigation changes as a whole (50% see changes, 50% do not)]
####Engineering notes
Consider if this will be wrapped up in an experiment or not (lean on current WMFExperimentsDataController for assigning and persisting buckets).
1. Add new navigation experiment enums to `Experiment`, `PercentageFileName`, `BucketFileName`, and `BucketValue` enums in WMFExperimentDataController.
2. Create a WMFNavigationDataController with two simple public methods, one for assigning the navigation experiment and one for pulling the navigation experiment assignment (control or test).
3. Add an WMFExperimentsDataController property to WMFNavigationDataController. Within WMFNavigationDataController public methods lean on WMFExperimentsDataController for determining and persisting assignments:
1. To assign an experiment call something like `try experimentsDataController.determineBucketForExperiment(.profileNavigation, withPercentage: 50)`
2. To check experiment assignment, call something like `return experimentsDataController.bucketForExperiment(.profileNavigation) == navigationProfileTest`
4. Call experiment assignment public method in WMFNavigationDataController somewhere in app launch sequence.
5. Wrap up UI changes & profile entry points (Settings, Explore, Article) by first checking WMFNavigationDataController to confirm they are a part of the test.