Create an async version of shared prefs

[kylecorry31]

In almost all (if not all) cases, I am not writing and directly reading a preference.

Therefore, I should be able to extend the cached preference to do the following:

• Asynchronously get all prefs when initially loaded
• Fall back to synchronous get when no cache hit (ex. before it is loaded / reloaded)
• On preference change, invalidate the cache for that pref + asynchronously reload the preference into cache

If the preference load is done on startup, in the background this should mean that most preference loads are cache hits.

• [ ] Update CachedPreferences to preload all preferences (preload flag)
• [ ] Update CachedPreferences to reload preference after it's changed
• [ ] Verify performance improvement
• [ ] Move GPS/steps cache to separate shared prefs