Merge skinning-15 to viewer-2. Fixes include:

DEV-35175 Spawning context menu should not move mouse cursor (Note: introduces regression where menu can fall off bottom of screen, will fix shortly)
DEV-35143 Modal alerts appear behind side tray
DEV-35141 Landmarks image and description outside of landmarks
Merging revisions 126418-126419,126726-126727,126856-126857,127010-127011,127014-127016 of svn+ssh://svn.lindenlab.com/svn/linden/branches/skinning/skinning-15 into G:\viewer-2.0.0-3, respecting ancestry