Provide getter/setter for NoTils/simple.Log.SHOW_LOGS switch

This is mainly to get a way to avoid the findbugs warning:

    Write to static field com.novoda.notils.logger.simple.Log.SHOW_LOGS from instance method xyz

Eventually this public static field should be demoted to private (breaking all projects in the process). Adding a deprecated flag for now to push people to migrate to the new accessor methods.
oh shoot, I thought that was only to explain _why_ something is deprecated. Do most IDEs pick up on it like this too? If so, wouldn't mind this as convention :+1: 

:shipit: