MAINT-2914 FIXED Mousing over UI elements does not make them light up

indra/llui/llcommandmanager.cpp

indra/llui/llcommandmanager.h

indra/llui/lltabcontainer.cpp

indra/llui/lltabcontainer.h

indra/llui/lltoolbar.cpp

indra/newview/app_settings/commands.xml

indra/newview/skins/default/textures/textures.xml

...iew/skins/default/textures/toolbar_icons/highlighting.png

indra/newview/skins/default/xui/en/panel_people.xml

indra/newview/skins/default/xui/en/widgets/tab_container.xml