EXP-1207 : merge with viewer-experience-fui

doc/contributions.txt

indra/llcommon/CMakeLists.txt

indra/llcommon/llfasttimer_class.cpp

indra/llcommon/llfasttimer_class.h

indra/llcommon/llinstancetracker.cpp

indra/llcommon/llinstancetracker.h

indra/llcommon/llsingleton.h

indra/llcommon/tests/llinstancetracker_test.cpp

indra/llcommon/tests/llsingleton_test.cpp

indra/llmessage/llcurl.cpp

indra/llmessage/llcurl.h

indra/llmessage/llpacketring.cpp

indra/llmessage/llpacketring.h

indra/llmessage/llproxy.cpp

indra/llmessage/llproxy.h

indra/llui/llbutton.cpp

indra/llui/llbutton.h

indra/llui/lllayoutstack.cpp

indra/llui/lllayoutstack.h

indra/llui/llnotifications.cpp