Adding a new visual param that allows users to manually adjust an offset for
how far off the ground (+ or -) their avatar's root bone is.
Supports the +-2m range people are used to adjusting in their viewers, but
new implementation should support server-generated appearances.
Conflicts:
indra/newview/character/avatar_lad.xml
indra/newview/llagent.cpp
indra/newview/llcallingcard.cpp
indra/newview/skins/default/xui/en/strings.xml