[settings] fix dealdlock in SettingsManeger introduced in #3512

As sugested by Montellese, using a shared lock fixes the deadlock in
SettinsManeger.
Merge pull request #3558 from huceke/fixups

[settings] fix dealdlock in SettingsManeger introduced in #3512
AE: re-add setting normalizelevels, formally inverted and known as boost volume on downmix
remove unused CProfilesManager::OnSettingsLoading()
videodb: remove commented out code
Merge pull request #3555 from FernetMenta/aefixes

AE: re-add setting normalizelevels, formally inverted and known as boost...
[rbp/omxplayer] Fix crash on stopping mp3 playback with amplification

There is a race condition where we can try to adjust volume after deinitialation
when amplification is enabled, causing a seg fault.
Merge pull request #3561 from popcornmix/amp_deinit_crash

[rbp/omxplayer] Fix crash on stopping mp3 playback with amplification