Squire asked me to route display name lookups via a simulator capability
using HTTP GET.  This buys us authentication until the data services team
can implement a public-facing authenticating web service for People API.

Reviewed with Simon

Also synchronize LLAvatarNameCache with server version
TODO: Get expiration time from web service

Plan is to use avatar profile pictures for these.

Also fixes a crash when turning on display names.

for slightly faster lookup times

Talks to web service so other people can see the change, but for now
they need to relog or toggle display names on/off to clear their
cache.

Stop pre-populated name cache because we have a web service now for lookup
Added mIsLegacy to LLAvatarName so we can colorize those name tags differently

code to turn them off

first attempt at "use display names" menu item which
doesn't work yet

Dang finicky LLSD map dereferences

Also removed unused LLComboBox globals to reduce llappviewer.cpp
include file burden.
Review pending

putting duplicate name in parentheses.

Changed LLUrlEntryAgent callbacks to handle both link label and icon
Eliminated legacy LLNameCache file loading
Reviewed with Kelly

well as LLAvatarName base data object.
Reviewed with Kelly.