[Practice] Repeated constant strings across code base

[Doomsdayrs]

I noticed that the application is using constant strings repeatedly throughout the code base. For example, org.asteroidos.sync.NOTIFICATION_LISTENER is typed in over and over again across the code.

This can be easily fixed by creating a constant value that all parts of the code can use. Which is most easy via kotlin where you can simply create a constants file that will hold all constants in the application