Update to linux_tools

Modernizes viewer_manifest.py
adds install.sh and refresh_desktop_app_entry.sh for those who want to "install" Singularity to their applications.
Updates client-readme-voice.txt to explain about Multi-Voice
File Menu Frosting~

Adds Minimize All, and Change Local Textures options
People keep adding how to do Local Textures, here's an easy way right where it'd be expected!
Group Feature Request: Optionally display indicator over typing avatar's heads.

Adds Debug Setting UseTypingBubbles
Adds "Use overhead typing indicator bubbles" to Adv. Chat-> Chat/IM
Thanks to Firestorm for this simple addition