Prototype code for "simple imposter" mode rendering of avatars.

indra/newview/app_settings/settings.xml

indra/newview/lldrawpoolavatar.cpp

indra/newview/llviewermenu.cpp

indra/newview/llvoavatar.cpp

indra/newview/llvoavatar.h

indra/newview/pipeline.cpp

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

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

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