Enable opening a New settings browser specific to an application

[hernanmd]

A method should be overridden to get one step closer to opening a new settings browser window, specific to an application settings. We should add:

StSettingsTree >> #nodeList
	| builder |
	^ nodeList
		ifNil: [
			builder := StSettingTreeBuilder new.
			self pragmasDo: [:p | builder buildPragma: p].
			nodeList := builder nodeList.
			nodeList do: [:n | n model: self].
			self checkForUnknownParent.
			self checkForUnknownTarget.
			self nodeList]

And we will be able to open application settings as this:

| setTree |
setTree := (StSettingsTree new acceptableKeywords: { #systemsettings }) nodeNamed: #fileBrowser.
(StSettingsMainPresenter newApplication: (StSettingsApplication new
		  useBackend: #Morphic;
		  yourself)) 
	rootNodes: setTree allChildren; " < ---- This also should be updated "
	open

Also, we should simplify the script.