ER-710:  Viewer effects.   Added 'lookAt' command for LLAgent event host API.  Also changed a bunch of parameters named 'event' to 'event_host' since VS highlights them as keywords.  Reviewed by Kelly.

Fixed a NULL pointer crash found while using viewer.  See https://osiris.lindenlab.com/viewer_crash_browser/index.php?filter_id=24941.  Reviewed by Kelly

ER-671: add llRegionSayTo().   Cleaned up some chat code, implemented '@' special case.  Reviewed by Kelly

ER-671: Add LLRegionSayTo() LSL function.  Added viewer preferences color picker under 'Colors' panel for messages sent directly to viewer via llRegionSayTo().  Reviewed by Kelly.

ER-671 : Add LLRegionSayTo() LSL function.  Added new chat type for direct messages to match server code, use light orange for text.  Reviewed by Kelly.

Use LLScrollListCtrl's intrinsic support for date-typed columns.