MAINT-8821: New "My Environments" floater. First pass.

indra/llinventory/llsettingsbase.h

indra/newview/CMakeLists.txt

indra/newview/llenvironment.h

indra/newview/llfloatereditextdaycycle.cpp

indra/newview/llfloaterfixedenvironment.cpp

indra/newview/llfloatermyenvironment.cpp

indra/newview/llfloatermyenvironment.h

indra/newview/llsettingsvo.cpp

indra/newview/llviewerfloaterreg.cpp

indra/newview/llviewermenu.cpp

.../newview/skins/default/xui/en/floater_my_environments.xml

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

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

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