Tweak detail settings and make graphics preferences widget enabling respect requirements.

indra/newview/app_settings/high_graphics.xml

indra/newview/app_settings/low_graphics.xml

indra/newview/app_settings/mid_graphics.xml

indra/newview/app_settings/settings.xml

indra/newview/app_settings/ultra_graphics.xml

indra/newview/featuretable.txt

indra/newview/llfloaterpreference.cpp

indra/newview/llviewercontrol.cpp

indra/newview/llviewershadermgr.cpp

indra/newview/llviewerstats.cpp

indra/newview/pipeline.cpp

...view/skins/default/xui/en/panel_preferences_graphics1.xml