Resolve "Upgrade SettingsService"

Closes #214 (closed)

SettingEntry now has the field subSettingIds to define a group of other settings. There exists a default group which will only come into play if there are other groups defined. Then all settings which have no group will end up there.

If groups are desired in any way they should be defined in a flavor's RccFeaturesModule. This currently is not the case.

You might want to test this by adding following code to RccFeaturesModule

const testSettingsEntryGroup: SettingsEntry	=	{
	id: 			'test_group',
	label:			'LABEL',
	description:	'DESCRIPTION',
	icon:			'',
	type:			'handler' as const,
	defaultValue:	null,
	subSettingIds:	['day-query-reminder']
}
[…]
	providers: [
		provideSettingsEntryGroup(testSettingsEntryGroup)
	]