LPS-36279 Refactor getControlPanelCategoriesMap to allow reusing the implementation

I left the new protected method in the wrong order to facilitate doing a diff. Will reorder in the next commit.
LPS-36279 Order method
LPS-36279 Add method getSiteAdministrationCategoriesMap
LPS-36279 Refactor JSP to use the new method
LPS-36279 Remove logic that is no longer necessary because it's already done in the Java logic
LPS-36279 When a user only has access to one portlet within Site Administrator hide the left menu
LPS-36279 Make sure the site selector is always shown as a menu
LPS-36279 SF
Lang keys