Medium sized update

1. Changed viewerres to update to new icon
2. Added Sliver.ico
3. Changed settings.xml to simply have an include for
settings_sliver.xml
4. Added settings_sliver.xml
5. Changed llStartup.cpp to have an include for vcFloaterHoo in the
event that I need it later
6. Changed llViewermenu.cpp - added some separators to the menu and put
the toggle for my test floater there
7. Changed llViewermessage.cpp to disallow people crashing you with Cat7
and Cat8 incoming inventory
8. Added vcFloaterHOO.xml / .cpp / .h