[EGD-3572] SettingsTable exchanged to Settings::Settings (#968)

[EGD-3572] Application has an instance of Settings - removed from derived apps
[EGD-3572] review issues resolved
[EGD-3572] shared_ptr -> unique_ptr
[EGD-3572] Primary Key for settings_tab:path
[EGD-3572] empty values handling
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