finish changes to update handling, including notices of channel changes

indra/newview/llappviewer.cpp

indra/newview/lllogininstance.cpp

indra/newview/llviewerwindow.cpp

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

indra/viewer_components/updater/llupdatechecker.cpp

indra/viewer_components/updater/llupdatechecker.h

indra/viewer_components/updater/llupdatedownloader.cpp

indra/viewer_components/updater/llupdatedownloader.h

indra/viewer_components/updater/llupdaterservice.cpp

...viewer_components/updater/tests/llupdaterservice_test.cpp