Refactor and optimize PreferencesHelper

[TacoTheDank]

I've refactored the PreferenceHelper to use a single sharedPreferences object initialized on app launch.

Benefits:

• No more passing a bunch of unnecessary contexts around.
• No more unnecessary operations where we create a brand new PreferenceManager.getDefaultSharedPreferences instance any time a key needs to be accessed.
  • We now register and unregister the same sharedPreferences object too

[y20k]

This is a really slick solution. I added you to the AUTHORS.md here (should have done earlier)

[TacoTheDank]

Thanks a lot! :)