Add UI Settings Group

[plemarquand]

Move the following settings in to their own group. Their ID does not change so there is no need to deprecate them or make code changes.

• swift.excludePathsFromPackageDependencies
• swift.showBuildStatus
• swift.showCreateSwiftProjectInWelcomePage
• swift.openAfterCreateNewProject

Issue #901

[award999]

Debugger and SourceKit-LSP settings put something in the setting ID. So we could add .userInterface to these settings (ex. swift.userInterface.showBuildStatus) to follow that theme and would show that category in the Settings editor (ex. Swift › User Interface: Show Build Status). Now 3 of these settings are fairly new so not quite as concerned about changing them as not too many people should have set, but swift.excludePathsFromPackageDependencies has been around a little longer so not sure how concerned we should be

[plemarquand]

Yeah I was hesitant to change the actual setting IDs as these settings have been released and so we'd need to maintain/migrate them. Does adding a segment to the ID have any benefit other than code clarity?

[award999]

Shows up marginally nicer in the Setting editor, ex. Swift › User Interface: Show Build Status

[adam-fowler]

This would mean we would have to deprecate the old settings and point people to the new ones. Unless we are making a significant gain I wouldn't bother changing them.