Preference to hide posts with few comments

[mosteo]

This is pretty barebones but my Android coding skills are somewhat rusty.

[QuantumBadger]

Thank you for this! The code looks good, I'll test before merging.

[QuantumBadger]

Before merging this I think it would be good to improve the user experience a bit, in terms of disabling this feature. Currently by default, Hide posts with few comments: -1 is shown in the settings if this is disabled. We should avoid using -1 for this -- I think it would be better to split this into two preferences: one for enabling/disabling (a CheckboxPreference), and one for setting the numeric limit (which is greyed out if the other preference is disabled).