Import Kitty Barnett/Catznip group chat disable feature with improvements

indra/newview/CMakeLists.txt

indra/newview/app_settings/settings_alchemy.xml

indra/newview/llagent.cpp

indra/newview/llgroupactions.cpp

indra/newview/llgroupactions.h

indra/newview/llgroupoptions.cpp

indra/newview/llgroupoptions.h

indra/newview/llimprocessing.cpp

indra/newview/llimview.cpp

indra/newview/llimview.h

indra/newview/llpanelgroupgeneral.cpp

indra/newview/llpanelgroupgeneral.h

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